Volatile Organic Compounds sensing properties of TbPc2 thin films: Towards a plasmon-enhanced opto-chemical sensor

Sensors and Actuators B 253 (2017) 266–274

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb

Volatile Organic Compounds sensing properties of TbPc2 thin films: Towards a plasmon-enhanced opto-chemical sensor Adriano Colombelli a,∗ , Michele Serri b , Matteo Mannini b , Roberto Rella a , Maria Grazia Manera a,∗ a

Istituto per la Microelettronica e i Microsistemi IMM sezione di Lecce, Via per Arnesano, 73100, Lecce, Italy Laboratory for Molecular Magnetism (LA.M.M.), Dipartimento di Chimica “Ugo Schiff”, Università degli Studi di Firenze and INSTM Research Unit of Firenze, Via della Lastruccia 3-13, 50019, Sesto Fiorentino, FI, Italy b

a r t i c l e

i n f o

Article history: Received 19 December 2016 Received in revised form 31 May 2017 Accepted 31 May 2017 Available online 10 June 2017 Keywords: Optical gas sensors Plasmonics Thin films Metallo-phthalocyanine Terbium

a b s t r a c t A sublimated film of double decker terbium(III) bis(phthalocyaninato) complex (TbPc2 ) has been tested for optical gas sensing applications. Morphological characterization of the sensing layer has been performed by atomic force microscopy. TbPc2 has been used as an opto-chemically interacting material to detect a class of volatile organic compounds (VOCs) following in real-time the UV–vis optical absorption variation. The interaction mechanism taking place between the investigated analytes and this double-decker-based thin films has been evaluated through the Freundlich isotherm. Additionally gold nanostructured plasmonic transducers grown onto glass substrate have been used as alternative functional substrate: the excitation of surface plasmon resonances at frequencies close to those of the bis-phthalocyanine molecular resonances has been investigated as a possible factor for increasing the sensing performances towards the investigated VOCs. By monitoring the shift of the typical localized surface plasmon resonance (LSPR) peak a plasmon-enhanced functionality is added and investigated thoroughly. © 2017 Published by Elsevier B.V.

1. Introduction During the past decade, metallo-phthalocyanines (MPc) have attracted considerable interest owing to their appealing photophysical, electronic and electrochemical properties [1–3]. They are widely used as the active material in processes driven by light due to their intense absorption in the visible, their excellent chemical stability upon illumination, and their relatively low cost. These properties have led to different applications ranging from chemical sensors to non-linear optical devices as well as inks, dyes and photodynamic therapy [4–7]. The sensing mechanism exploits the rearrangement of the electrical dipole in the thin film resulting from the interaction between phthalocyanine and the analytes. A reversible change of the distribution of highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) takes place in thin films of phthalocyanine compounds due to the presence of oxidizing gases as well as via van der Waals interactions or coordination of the ana-

∗ Corresponding authors. E-mail addresses: [email protected] (A. Colombelli), [email protected] (M.G. Manera). http://dx.doi.org/10.1016/j.snb.2017.05.183 0925-4005/© 2017 Published by Elsevier B.V.

lyte to the MPc. These changes can be probed both optically, by UV visible absorption spectroscopy, and electrically through changes in the charge carrier mobility in the thin film [8,9]. Chemical selectivity can be additionally ensured in these systems via manipulation of the metal center and substitution of functional groups on the organic ring [10–15]. In order to create solid state optical sensors, thin films of metal phthalocyanines have been prepared by physical or chemical methods, such as vapor deposition, spin coating and LangmuirBlodgett (LB) deposition techniques [16–18]. These strategies have been tested also for several derivatives of MPc systems, the most common substituents being alkyl, alkoxy or alkoxymethyl chains [19,20]. Adsorption of several organic vapors derivatives in MPc derivatives were studied using QCM (Quartz Crystal Microbalance), ellipsometry and SPR (Surface Plasmon Resonance) experimental techniques. These adsorption process are usually very fast, and full recovery of the sensing film has been observed after flushing with clean air. These effects are attributed to weak and non-specific interactions between guest molecules and the organic thin films, including capillary condensation through their surface pores and eventually a partial swelling with high concentration analytes [21]. The reactivity towards electron donors or electron acceptors is of special interest in the case of the bis(phthalocyaninato) rare

A. Colombelli et al. / Sensors and Actuators B 253 (2017) 266–274

Fig. 1. Molecular structure of TbPc2.

earth compounds LnPc2 (with Ln = Tb, Yb, Lu, Eu, Gd) [22–25], which form double decker systems featuring the presence of two macrocyclic ligands enclosing a trivalent lanthanide ion. Intensive research activity has been devoted to this family of organometallic systems for potential device applications due to their high intrinsic conductivity and electrochemical and electrochromic properties [26]. The neutral form LnPc2 possesses a radical delocalized on the ␲-conjugated macrocycles as demonstrated by electron spin resonance studies [27,28]. All LnPc2 complexes and related doubledeckers normally undergo multiple reversible reductions of the ␲-orbitals of the conjugated macrocycle and a single reversible oxidation when dissolved in non-aqueous media [29,30], where each redox state is characterized by different optical, electrical and magnetic properties [31]. The discovery of single molecule magnet behavior in the Tb(III) bis-phthalocyaninato complexes compound has prompted the investigation of double decker systems also in the field of molecular spintronics [32,33]. The production of thin films of these complexes has stimulated the development of novel sensing device structures by exploiting the changes in physicochemical properties of LnPc2 systems caused by their ambient environment [22]. Since these molecules have particularly high intrinsic conductivities (␴=10−6 –10−3 S/cm at T = 300 K) [34,35] and their reactivity towards electron donor or electron acceptor gases is particularly interesting, their possible applications as sensitive materials have been less investigated compared to MPcs-based sensors. The UV–vis absorption spectra of the LnPc2 LB films have been successfully used for the detection of strong electron donor or acceptor gases, and the capabilities of these films to detect weak electron donor or acceptors such as volatile organic compounds (VOCs), including alcohols, aldehydes, esters and acids that are responsible for the aromas of foods and beverages, have also been demonstrated, although to a lesser extent [36]. These results have opened the possibility of using thin films of LnPc2 as sensing units in electronic noses for the detection of aromas [37]. In this work, thin films of TbPc2 (Fig. 1) have been sublimated directly on pristine glass substrates as well as on glass surfaces decorated with “naked” gold nanoparticles. Sublimation guarantees a reproducible open structure with a high surface/volume ratio, allowing the presence of a high number of absorption sites for the interaction of the vapors with the active layer [38,39], as demonstrated by the morphological characterization of the resulting thin films carried out by atomic force microscopy. Exposure of the TbPc2 sensing layers to various volatile organic compounds in a controlled atmosphere induced variations in the typical absorption peaks, which have been exploited for the detection of the target analytes. Sensitivity toward the investigated analytes has been calculated and an explanation of the possible mechanism of interaction has been proposed. The motivation behind the deposition of the sensing layer onto metal nanostructures-decorated glass substrates is related to the idea of exploring the possibility to add an active functionality to the

267

substrate by illuminating in a proper spectral range with the aim to improve the sensing layer performance upon interaction with the investigated analytes. Analogue ideas have been surveyed in the literature in different ways: Burlachenko et al. [40] explored the possibility to enhance discriminating capacity of electronic nose systems by using a spectrally selective illumination of a photosensitive sensor coating in cross-selective chemical sensor arrays. Different investigations demonstrated enhanced gas sensitivity of thin film semiconductor sensors under UV illumination [41]. In this work metal nanostructures grown by physical methodologies onto glass substrates have been used as substrates for the subsequent deposition of the double −decker thin film. When noble metal nanoparticles interact with incident electromagnetic waves, their optical response is the excitation of Localised Surface Plasmon Resonances (LSPR) due to the collective oscillation of the free-electrons leading to highly localized electromagnetic fields at the nanoparticles surface and to intense absorption bands that are absent in the bulk or flat surfaces [42,43]. Such optical spectra are strongly affected by the particle size and shape as well as changes in the local refractive index that accompanies molecular binding on the plasmonic nanostructures or on thin sensing overlayers. Besides, recent studies revealed that strong coupling between the plasmonic resonances of metal nanoparticles and molecular transitions of an adsorbate can occur depending on the spectral overlap of the two, thus allowing to study in depth the electronic structure of the molecule and its possible changes by monitoring the absorption spectrum [44]. Here, the excitation of localized plasmon resonances of metallic nanostructures at wavelengths close to the absorption range of the TbPc2 sensing adlayer is investigated as an external stimulus able to amplify its sensing response towards a selection of the investigated VOCs gas molecules. The two phenomena, either the coupling between plasmonic and molecular resonances of the terbium double decker thin film or the occurrence of surface-enhanced optical functionalities due to the intense electromagnetic fields around the metal nanostructures, are investigated to explain the twofold improvement of the sensing performance of the plasmon-enhanced chemical sensor.

2. Experimental section The neutral TbPc2 complex, has been synthesized according to the De Cian procedure slightly modified to increase the yield of the reaction [45]: a mixture of 1,2-dicyanobenzene (15,6 mmol), Tb(OAC)3 .·4H2 O (1 mmol) and 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) (8 mmol) in 50 mL of 1-hexanol has been refluxed for 1.5 days. The solution has been cooled to room temperature and then filtered. The resulting dark purple crystalline precipitate has been treated successively with acetic anhydride, cold acetone, npentane and then dried in air. The purple crystalline precipitate has been extracted with several portions of chloroform, concentrated under vacuum with a rotary evaporator and purified using column chromatography of silica gel using a 2% CH3 OH/CH2 Cl2 as eluent. The microcrystalline powder has been subsequently purified by heating up to ca 300 ◦ C the powder in a vacuum chamber by using an home-made Joule-heated Knudsen cell until optimal vacuum condition are achieved (low 10−7 mbar). The obtained purified TbPc2 has been sublimated at ca. 450 ◦ C on quartz substrates producing 200 nm thick films in high vacuum, using a quartz microbalance to control the deposition rate. According to previous reports [46,47] TbPc2 molecules on the topmost layers of the deposit are expected to be preferentially oriented in a standing configuration in a thick film. The surface morphology of the molecular films has been investigated in air at room temperature by atomic force microscopy (AFM), using NSC-36 cantilever probes (Mikro-

268

A. Colombelli et al. / Sensors and Actuators B 253 (2017) 266–274

Fig. 2. (a) AFM image of a 120 nm TbPc2 thermally evaporated thin film. (b) UV–vis absorption spectra of a TbPc2 thin film (thickness 120 nm). Scale bar corresponds to 200 nm.

Masch, Tallinn, Estonia) with resonance frequency of 125 kHz on a P47-PRO microscope (NT-MDT Co. Zelenograd, Moscow, Russia). Semi-contact mode has been used to minimize deformations of the soft molecular structure. To enhance the sensing performance, substrates containing gold nanoparticles realized by de-wetting process were also adopted for the deposition of TbPc2 films. The detail of the preparation of this plasmonic transductor has been reported elsewhere [48] together with the relative structural and morphological characterization. Since the plasmonic field enhancement rapidly decays with the distance, thinner TbPc2 films of 23 nm and 33 nm were thermally deposited in vacuum onto the substrates covered by gold nanoparticles, in order to optimize the sensitivity to the analytes. UV–VIS absorption spectra of thermally evaporated TbPc2 thin films both on bare quartz or plasmonic nanostructures have been measured by using a Varian Cary 500 UV–vis-NIR spectrophotometer. All the optical sensing tests have been carried out at room temperature and at normal incidence of the light beam using a filtered light source from an AVANTES tungsten-halogen lamp guided into an optical fiber. The absorption spectra, in the range corresponding to the Q-band of TbPc2 , have been collected and analyzed using a commercial spectrophotometer (AVANTES model MC 2000). Recording of the dynamic responses relative to different spectral ranges is possible by such experimental setup. The light beam power illuminating the sensing layer is very low, (dozens of ␮W, as confirmed by the manufacturer), therefore, we are reasonably confident that effects on the temperature of the sensing layer due to illumination are negligible. The effect of the investigated vapors on the absorption properties of the active layer has been measured in a dynamic pressure system implemented in our laboratory where dry air at ambient pressure has been used as carrier and reference gas. Details of the home-made experimental setup are reported in ref 3. 3. Results and discussion Fig. 2a reports the AFM characterization of a 120 nm TbPc2 film deposited onto a quartz substrate, having analogous morphology to those of the thicker 200 nm films used later for sensing. These film present moderate average roughness (RMS of c.a. 4.75 nm in a 1 ␮m x 1 ␮m area), evidencing the presence of elongated grains that are ca. 120 nm long and ca. 40 nm wide. This morphology is different from the spherical grain shape typical of ␣ phase MPc films [49] evaporated at room temperature and shows instead some similarities with the ␤ phase films [50], suggesting that the ␣ phase is less stable in TbPc2 films. Fig. 2b shows the optical absorption spectrum of a typical neutral TbPc2 thin film deposited onto the same substrate. The spectrum exhibits the characteristic absorption bands of doubledecker phthalocyaninato complexes [45] which show an intense

green colour. The conjugated ␲ systems of each LnPc2 in the neutral form features intense absorption bands in the UV–vis range, which are typically described by two main bands assigned to ␲→ ␲* transitions, the Q band centered at about 640–690 nm (which is responsible for the blue or green colour of the compound) and the Soret-band centered at about 320–350 nm. The position of the Q band is modified to some extent by the nature of the central ion and by the presence of substituents. The Q band results from the promotion of electrons from the first semi-occupied molecular orbital to the second lowest unoccupied molecular orbital (LUMO) and from the second fully occupied highest occupied molecular orbital (HOMO) to the first LUMO. Furthermore, the spectrum shows a typical Soret-band, resulting from the electronic transitions from the third occupied HOMO to the first LUMO, with maxima at 329 nm. The weak ␲-radical band at 469 nm is due to electronic transitions from the semi-occupied molecular orbital to the degenerate LUMOs [51]. In order to test the sensing parameters of these active macrocycles, the dynamical changes of the integral area of the Q band absorption peak (600–750 nm), which comprises the lowest energy HOMO-LUMO transitions, has been recorded versus time during the interaction with the VOCs vapors. This integral acts as an enhanced response parameter, with respect to a single-wavelength absorbance monitoring, because of the extended interval of wavelengths in the UV–vis spectral range (␭ ∼ = 150 nm) [39]. To this purpose measurements have been carried out by exposing the sensor to the vapors-dry air mixture for 5 min, followed by a recovery period of 5 min in dry air. The typical reversible dynamic responses obtained during exposure to ethanol, hexanol, isopropanol and methanol vapors are reported in Fig. 3a which shows that significant changes of the integrated absorption occur during exposure to analyte vapors. It can also be seen that the change of the signal as a function of concentration is not the same for all the alcohols. Similar behavior is observed in the presence of different classes of VOCs analytes. Fig. 4a shows dynamical responses recorded in the presence of acetic acid, butylamine, ethyl acetate and butyraldehide mixed in dry air at different concentrations at room temperature. Also in this case a reversible signal is demonstrated. The maximum vapors concentration formed in a closed test chamber can be calculated by dividing the vapor pressure at the working temperature by the atmospheric pressure. In order to investigate the same concentration range, proper dilutions of saturated vapors in a dry-air flux were set. Concentrations values ranging between 5 × 103 ppm and 1 × 104 ppm were achieved for ethanol, methanol and isopropanol vapors; lower concentrations are obtained for hexanol vapors owing to lower vapor pressure. The spectral response of the sensor was then analyzed quantitatively to understand the mechanism of interaction with the analyte. We assumed that the change of the integral optical absorption I varies proportionally to the number of adsorbed gas molecules on

A. Colombelli et al. / Sensors and Actuators B 253 (2017) 266–274

Fig. 3. a) Typical dynamic responses of the analyzed optical spectral range recorded at room temperature in the presence of ethanol, isopropanol, methanol and hexanol vapors. b) corresponding calibration curves.

the phthalocyanine surface [VOCs ]ads . Furthermore, it is assumed that the fraction ␪ of surface covered by the VOC analyte follows the Freundlich adsoption isotherm: ␪ = kP x

(1)

where P is the partial pressure of the analyte vapor in the test chamber and k and x are constants [52]. This model implies that the investigated VOCs molecules are weakly adsorbed on phthalocyanine molecules and that the activation energy for the adsorption process increases linearly with surface coverage. Obviously, it has been assumed that the number of the adsorption sites is constant and that the surface adsorption is not assisted, at the same time, by diffusion into the bulk of the film. Since I and the number of adsorbed molecules [VOCs ]ads are proportional to ␪, and P, in turn, is proportional to the concentration CVOCs of the investigated VOC in the gas mixture, the dependence of the optical absorption versus gas concentration is well described by the relation a I ∝ CVOCs

(2)

where ␣ depends on the stoichiometric coefficients of the equilibrium reaction taking place during the interaction between phthalocyanine macromolecules and chemisorbed VOCs molecule [53]. Additionally, from Eq. (2) one should expect a linear plot of I with respect to concentration of VOCs in a log–log scale with the slope of the line corresponding to the value of ␣· Measurements of the integral optical absorption change (I) in the investigated spectral range, carried out onto our TbPc2 film at different analyte concentrations, have shown that the optical absorption grows with increasing VOCs concentration. Figs. 3 b and

269

Fig. 4. a) Typical dynamic responses of the analyzed optical spectral range in the presence of different concentration of acetic acid, butylamine, ethyl acetate and butyraldehide vapors mixed in dry-air in the test chamber at room temperature. Concentration values were calculated by proper dilution of saturated VOC’s vapors in the same ppm range. b) Calibration curves corresponding to the TbPc2 –based thin sensing layer exposed to different concentration of (butylamine, ethyl acetate, butyraldehide and acetic acid mixed in dry-air at room temperature.

4 b show on log–log plots the I responses vs. gas concentration towards the investigated analytes carried out at room temperature, exhibiting the expected linear relationship. The slope of the curve reported in Figs. 3 b and 4 b gives information about the ␣ parameter linked to the VOCs/TbPc2 reversible chemical reaction. Higher ␣-values implicate higher sensitivity or reactivity of the sensing layer towards VOC investigated analyte (Table 1). Finally, the histogram reported in Fig. 5 highlights that the reactivity of the investigated active layer is more pronounced towards alcohols and esters or aldehydes compared to the other classes of analytes of interest in food analysis. Further investigation aimed at improving the optochemical transduction performance of the sensor was achieved by adding an active functionality to the substrate hosting the TbPc2 sensing layer. It is known form literature that when resonant molecules are adsorbed on the nanoparticles, coupling between the molecular resonance and nanoparticle LSPR can occur, as it has been observed experimentally and simulated by electrodynamics theory [54,55]. The induced LSPR shift due to this coupling is found to be strongly dependent on the spectral overlap between the molecular resonances and the LSPR [56]. To this purpose, an active plasmonic transducer, consisting in gold nanostructures deposited onto glass substrates and covered of a very thin TbPc2 sensing layer, has been introduced. The morphology of the plasmonic structures covered by a 23 nm layer of TbPc2 is shown in Fig. 6a, in which it is possible to identify individual nanoparticles. To explore the morphology of TbPc2 film in this thickness range without the interference of the topography of the nanoparticles array, a film of 40 nm was grown

270

A. Colombelli et al. / Sensors and Actuators B 253 (2017) 266–274

Table 1 Investigated analytes for food analysis application and corresponding ␣ parameters. Classes

Alcohols

Acids

Alkanes

Aliphatic amines

Esters

Aldehydes

Analyte ␣

MeOH EtOH iPrOH 1.16 1.07 0.68

AcOH 0.66

HexOH 0.72

Butylamine 0.64

Ethyl acetate 1.35

Butirraldeide 1.37

Fig. 5. Histogram of the ␣-values related to the reactivity of TbPc2 molecules towards the investigated analytes.

Fig. 6. AFM images of TbPc2 films evaporated on a substrate covered by gold nanoparticles (a), and on glass (b). The film thickness is 23 nm in (a) and 40 nm in (b). Scale bar in both images corresponds to 200 nm.

on glass and measured by AFM. The film structure in Fig. 6b, which can be assumed to be similar to the one of TbPc2 films on nanoparticles, is characterized by a low roughness (Root mean square, rms 1.5 nm) and irregular grains with a typical size of 40 nm, in contrast with the behavior observed in the thicker film (Fig. 2a). The plasmonic excitation of LSPR resonances should give to the transducer an active functionality able to amplify and improve the sensing response of the adsorbate layer deposited over it. Fig. 7 shows the typical optical absorption peaks of doubledecker TbPc2 thin films deposited onto a nanostructured gold transducer. Besides the typical absorption band of the TbPc2 thin films, an additional optical absorption peak is recorded at about 550 nm, due to the excitation of the LSPR of the gold nanostructures. A wavelength red-shift (nearly 20 nm) of the LSPR peak is shown in Fig. 7 upon the deposition of a thin layer of TbPc2 : this behavior is ascribed to a change in the refractive index of the environment surrounding the surface metal nanostructures due to the presence of the TbPc2 adlayer. Upon interaction of the organic layer with the investigated vapors molecules, further changes in its refractive index are expected both in the real or the imaginary component: they can be detected in real time by monitoring the changes in the two absorp-

tion peaks, the LSPR and the TbPc2 Q-band, characterizing the new composite structure. As a proof of concept, ethanol alcohol vapors has been selected as analyte sample. Fig. 8a shows the dynamic sensing signal in the 600–750 nm spectral range, corresponding to the absorption bands of a TbPc2 thin film deposited onto the plasmonic transducer, when increasing concentrations of ethanol vapors are sent into the test chamber separated by a purging flux of dry air to ensure recovering of the sensing layer. The corresponding calibration curve is reported in red in Fig. 8b. For the sake of comparison, the calibration curves for the bare TbPc2 sensing layer deposited onto clean glass substrate recorded within the 600–750 nm spectral range at increasing ethanol vapors concentration is reported as well in Fig. 8b. It is worth to observe that, although acquired in the same spectral region and with the same sensing layer, the two experimental conditions are quite different: in the first case the sensor signal is acquired upon LSPR excitation of the underneath transducer (red), while in the second case the sensor signal is acquired without any optical contribution of the glass substrate (black). From the slope of the calibration curves recorded within the same spectral range, an increase in the sensor response as well as in the sensitivity parameters can be evidenced for the plasmon acti-

A. Colombelli et al. / Sensors and Actuators B 253 (2017) 266–274

Fig. 7. Typical UV–vis absorption spectra of the bare Au NPs plasmonic transducer and TbPc2 thin film obtained by thermal evaporation from the synthetized TbPc2 powder deposited on top of the plasmonic transducer.

vated TbPc2 layer. This can lead to the conclusion that the plasmonic transducer can have an active and beneficial role in the interaction between the organic adlayer and the investigated analyte due to the plasmon excitation in a spectral region close to the electronic transition of the TbPc2 . It is known that a consequence of the LSPR excitation condition in metal nanostructures by the electromagnetic radiation of proper energy, is the formation of enhanced electromagnetic fields that extend from the nanostructured surfaces to tens of nanometers above its surface. When resonant molecules are adsorbed on the nanoparticles the excitation of the surface plasmon greatly increases the local field experienced by the molecule. Strong and confined electromagnetic field induced by the metal nanoparticle can polarize the molecule [57]. If the molecule has resonant absorbance overlapping with surface plasmons, optical responses of both the molecules and the plasmonic nanostructures are changed by their mutual interaction. Overlapping plasmonic and electronic resonances can also lead to pronounced dips or splitting in the plasmon resonance spectrum due to plasmon resonant energy transfer or plasmon hybridization [58]. When plasmon and molecules are weakly overlapped, as it is in this case, metal nanostructures behave as passive antennas that may drastically amplify the molecular optical cross sections but which are themselves not strongly influenced by the interaction. In 2006, Van Duyne research group [54] showed that a molecule with an electronic resonance close to the plasmon resonance of a nanoparticle substrate could generate a significantly different plasmon resonance shift response. The origin of this effect could be due to the wavelength-dependent polarizability of the adsorbed molecules either constructively or destructively interfering with the plasmon modes of the nanostructures, leading to either enhanced or suppressed plasmonic shifts, respectively.

271

In our case, the sensing material is characterized by the presence of delocalized ␲-electrons system which constitutes a highly polarizable electronic cloud producing intense dispersion forces between adjacent molecules of phthalocyanine exhibiting ability to enter reversible interaction with investigated analytes. The high wavelength shift of the LSPR plasmon peak upon evaporation of the TbPc2 sensing layer suggests that, according to Van Duyne and coworkers results, we are in the condition of a positive change in the sensing layer polarizability, which can effectively influence the dipole moment of the interacting alcohol vapors molecules and induce a measurable but reversible dipole–dipole interaction between them. The increase in the absorption peak upon interaction with ethanol vapors (Figs. 3 and 8 a) gives account of the reducing behavior of the investigated analyte thus reinforcing the polarizable behavior of the electronic cloud. Further elements of comprehension on the effect of such local e-m field enhancement on the sensing mechanism can be achieved by investigating its effect on the refractive index changes of the sensing adlayer upon adsorption of alcohol vapors. Both real and complex component of the refractive index have to be taken into account as the first is related to packing density changes of the sensing layer and the latter is more strictly related to changes in its electronic state due to chemical interaction with the investigated analytes. As evidenced above, this can be experimentally achieved by recording the integral area below the two absorption peaks evidenced in the composite Au transducer- TbPc2 samples (Fig. 8a), upon interaction with increasing concentration of a selected alcohol vapors. To this purpose, Fig. 8b and c report the calibration curves related to the sensor responses towards ethanol vapors recorded upon selection of the high wavelength peak (600–750 nm) and of the low wavelength peak spectral region (500–610 nm), respectively. The first is in the same range of the characteristic Q band observed also in the bare TbPc2 layer deposited onto transparent glass substrate, the latter, red shifted with respect to the plasmon resonance band, well describes the change in the real part of the sensing layer refractive index. It is worth to note that the results reported in both figures (Fig. 8b and c) are recorded with sensing sample completely highlighted by white light coming from the lamp, so that LSPR excitation is guaranteed in both cases, while the reported spectral range is related only to the selected region where the integral area is recorded during the sensing test. Observation of the calibration curve in the low wavelength spectral range (black points) leads to the conclusion that there is a good correlation between the sensor responses to alcohols and their respective saturated vapor pressures which may indicate the mechanism of capillary condensation of alcohol vapors in nano-porous film structure [21]. An obvious indication of that mechanism is weak binding of the analyte molecules which results in a fast sensor response and equally quick recovery. In this kind of process, multilayer adsorption from the vapor phase occurs until the point at which pore spaces become filled with condensed liquid from the vapor phase and this occurs below the saturation vapor pressure of the pure liquid. An experimental consequence is a remarkable change in the density, namely in the real part of the refractive index of the sensing layer, which is well described by the sensor response relative to low wavelength spectral range (Fig. 8c, black). In addition, the effect of the thickness of the sensing layer in this process has been investigated in Fig. 8c, (red points) by monitoring the refractive index-related band of a thicker layer of TbPc2 molecules deposited onto an analogous plasmonic transducer. In fact, above 20 nm of thickness, the sensing performances seems to be spoiled and this can be reasonably explained by considering that if the TbPc2 layer thickness is higher with respect to the penetration depth of the LSPR (typically 10–20 nm), the binding event with the gas molecule occurs far from surface probing region. Consequently,

272

A. Colombelli et al. / Sensors and Actuators B 253 (2017) 266–274

Fig. 8. a) Typical dynamic sensing curve due to the interaction of ethanol VOCs ad TbPc2 active layer deposited onto gold nanoparticles transducers acquired in the 600–750 nm spectral range. b) Calibration curves obtained in the 600–750 spectral range by using TbPc2 with and without plasmonic transducer. c) Calibration curve obtained in the 500–610 nm spectral range by using two different TbPc2 thickness deposited onto plasmonic transducer. The coefficient ␴ is the sensitivity calculated as slope of the linear part of the calibration curve.

the LSPR sensing signal is not able to follow the dynamic variation of the refractive index and sensitivity tends considerably to decrease. In conclusion, we can rationally deduce that the sensing mechanism is strictly related to the high polarizability of the double decker adlayer upon the effect of LSPR excitation. This effect translates into a consequent higher probability of interaction with vapor molecules being themselves influenced by the effect of this enhanced e-m field generation at the metal/sensing layer interface due to their measurable dipole moment. Further vapor molecules adsorption can lead to multilayer formation with consequent changes in the refractive index of the macrocycle sensing layer. The major contribution is not related to the porosity or the thickness of the sensing layer while on the effect of the excitation of LSPR resonances, as the sensing behavior of TbPc2 layer deposited on glass, which reports and higher roughness is less performant of the composite LSPR-TbPc2 sensing layer upon LSPR excitation. The above discussion has allowed identifying a new strategy for improving sensing performances of a TbPc2 layer by adding an active functionality on the substrates. The monitoring of the absorption band typical of the investigated macrocycle layer upon LSPR excitation could represent a valid method for achieving high sensitivity values. Although experimented here for a particular analyte, the approach is likely to be valid for a series of VOCs vapors paving the way to new perspectives in the field of optical sensing by using metallo-phtalocyanine-based sensors.

Further insights could be pursued in order to investigate the effect of vapor molecules characterized by different size, refractive index and polarizability, as well the effect of sensing layers whose spectral features overlaps with the plasmon resonances. 4. Conclusions In this work we reported on the opto-chemically sensing properties of TbPc2 sublimated thin film. The analysis of the responses emphasizes a reversible and reproducible sensor signal towards different concentrations of the investigated VOCs vapors. In order to extract more information from the absorption spectra and their changes in the presence of vapors, we analyzed the variation in the time of the area integral corresponding to the typical absorption peaks in the 600÷750 nm spectral range. Interestingly we noticed an influence of the analyte in the absorption. Further study concerning the optimization of the thin layers in terms of stability, sensitivity, selectivity, response and recovery time will be the object of our future investigation. To this purpose, preliminary studies performed onto an innovative transducer realized by using gold nanostructures distributed onto planar surface and covered by TbPc2 sensing layer has been suggested. The monitoring of the Q band typical of the investigated macrocycle layer upon LSPR excitation after interaction with a particular alcohol vapors has demonstrated an increase in the sensing performance with respect to the bare TbPc2 layer. The existence of intense local elec-

A. Colombelli et al. / Sensors and Actuators B 253 (2017) 266–274

tromagnetic fields around the metal surfaces, due to excitation of the plasmon modes, is reasonably responsible of the investigated surface-enhanced functionality. Additional efforts in this perspective could ensure great flexibility in the choice of sensing layers and of the proper material and nanostructures for plasmonic transducers. The optimization of the metal nanostructures shapes and sizes as well as of the sensing adlayer with proper molecular resonances moreover might allow studying more in depth the effect of the coupling of molecular and plasmonic resonances opening novel routes for enhanced optical gas sensing in different spectral ranges. Funding sources This work has been funded by the Italian MIUR through the FIRB project “NanoPlasMag” (RBFR10OAI0). Dr. Michele Serri acknowledges funding by EC through FP7-People-2011-IAPP (286196) ESN-STM. Acknowledgments Many thanks are due to Mr. F. Casino and Mrs. C. Martucci for skilful technical assistance in the optical experimental set-up arrangement. B. Cortigiani and D. Rovai are fully acknowledged for their technical support during the preparation of the samples.

[20]

[21] [22] [23]

[24]

[25]

[26]

[27]

[28]

[29]

References [30] [1] N.B. McKeown, Phthalocyanine Materials: Synthesis Structure and Function, Cambridge University Press, Cambridge, 1998. [2] C.C. Leznoff, A.B.P. Lever, Phthalocyanines: Properties and Applications, 1–4, VCH Publishers, New York, 1989–1996. [3] J. Simon, J.J. Andre, Molecular Semiconductor, Springer, Berlin, 1985. [4] N. Kobayashi, Optically active phthalocyanines, Coord. Chem. Rev. 219–221 (2001) 99–123. [5] K. Lang, J. Mosinger, D.M. Wagnerová, Photophysical properties of porphyrinoid sensitizers non-covalently bound to host molecules; models for photodynamic therapy, Coord. Chem. Rev. 248 (2004) 321–350. [6] J.J. Doyle, J. Wang, S.M. O’Flaherty, Y. Chen, A. Slodek, T. Hegarty, L.E. Carpenter, D. Wöhrle, M. Hanack, W.J. Blau, Nonlinear optical performance of chemically tailored phthalocyanine–polymer films as solid-state optical limiting devices, J. Opt. A: Pure Appl. Opt. 10 (2008) 075101. [7] J.P. Mensing, A. Wisitsoraat, A. Tuantranont, T. Kerdcharoen, Inkjet-printed sol?gel films containing metal phthalocyanines/porphyrins for opto-electronic nose applications, Sens. Actuators B 176 (2013) 428–436. [8] B. Bott, S.C. Thorpe, Techniques and Mechanisms Gas Sensing, in: P.T. Moseley, J. Norris, D.E. Williams (Eds.), Adam Hilger, Bristol, 1991. [9] M. Bouvet, P. Gaudillat, J.-M. Suisse, Phthalocyanine-based hybrid materials for chemosensing, J. Porphyr. Phthalocyanines 17 (2013) 913–919. [10] M.L. Rodríguez-Méndez, in: Craig. S. Grimes, Elizabeth C. Dickey, Michael V. Pishko (Eds.), Sensing Properties of Phthalocyanines in Encyclopedy of Sensors, vol. 9, American Scientific Publishers, California, USA, 2006, pp. 111–134 (ISBN: 1-58883-056-X.). [11] F.I. Bohrer, A. Sharoni, C. Colesniuc, J. Park, I.K. Schuller, A.C. Kummel, W.C. Trogler, Gas sensing mechanism in chemiresistive cobalt and metal-Free phthalocyanine thin films, J. Am. Chem. Soc. 129 (2007) 5640–5646. [12] T. Basova, A. Hassan, F. Yuksel, A.G. Gürek, V. Ahsen, Optical detection of pentachlorophenol in water using thin films of octa-tosylamido substituted zinc phthalocyanine, Sens. Actuators B 150 (2010) 523–528. [13] A.W. Snow, W.R. Barger, in: C.C. Leznoff, A.B.P. Lever (Eds.), Phthalocyanines: Properties and Applications, vol. 1, VCH Publishers, New York, 1989, pp. 341–392. [14] R.D. Gould, Structure and electrical conduction properties of phthalocyanine thin films, Coord. Chem. Rev. 156 (1996) 237–274. [15] K.J. Albert, N.S. Lewis, C.L. Schauer, G.A. Sotzing, S.E. Stitzel, T.P. Vaid, D.R. Walt, Cross-Reactive chemical sensor arrays, Chem. Rev. 100 (2000) 2595–2626. [16] M.L. Rodríguez-Méndez, C. Apetrei, J.A. de Saja, Evaluation of the polyphenolic content of extra virgin olive oils using an array of voltammetric sensors, Electrochim. Acta 53 (2008) 5867–5872. [17] V. Parra, Á.A. Arrieta, J.A. Fernández-Escudero, M.L. Rodríguez-Méndez, J.A. De Saja, Electronic tongue based on chemically modified electrodes and voltammetry for the detection of adulterations in wines, Sens. Actuators B 118 (2006) 448–453. [18] T. Komeda, K.K.M. Yamashita, Double-decker phthalocyanine complex: scanning tunneling microscopy study of film formation and spin properties, Prog. Surf. Sci. 89 (2014) 127–160. [19] N. Sheng, R.J. Li, C.F. Choi, W. Su, D.K.P. Ng, X.G. Cui, K. Yoshida, N. Kobayashi, J.Z. Jiang, Heteroleptic bis(phthalocyaninato) europium(III) complexes fused

[31]

[32]

[33]

[34]

[35] [36]

[37]

[38] [39]

[40]

[41]

[42] [43] [44]

[45]

[46]

[47]

273

with different numbers of 15-crown-5 moieties. Synthesis spectroscopy, electrochemistry, and supramolecular structure, Inorg. Chem. 45 (2006) 3794–3802. X.Y. Wang, Y.L. Chen, H.G. Liu, J.Z. Jiang, Spectroscopic and structural characteristics of Langmuir-Blodgett films of bis[2,3,9,10,16,17,24,25-octakis(octyloxy)phthalocyaninato] rare earth complexes, Thin Solid Films 496 (2006) 619–625. A.V. Nabok, A.K. Hassan, Asim K. Ray, Condensation of organic vapours within nanoporous calixarene thin films, J. Mater. Chem. 10 (2000) 189–194. J.A. de Saja, M.L. Rodriguez-Mendez, Sensors based on double-decker rare earth phthal ocyanines, Adv. Colloid Interface Sci. 116 (2005) 1–11. Y.L. Chen, H.G. Liu, N. Pan, J.Z. Jiang, Langmuir?Blodgett films of substituted bis(naphthalocyaninato) rare earth complexes: structure and interaction with nitrogen dioxide, Thin Solid Films 460 (2004) 279–285. K.L. Trojan, J.L. Kendall, K.D. Kepler, W.E. Hatfield, Strong exchange coupling between the lanthanide ions and the phthalocyaninato ligand radical in bis(phthalocyaninato) lanthanide sandwich compounds, Inorg. Chim. Acta 200 (1992) 795–803. M.L. Rodrı´ıguez-Méndez, R. Aroca, J.A. de Saja, Spectroscopic and electrochemical properties of thin solid films of Yttrium bisphthalocyanine, Spectrochim. Acta 49A (1993) 965–973. R. Weiss, J. Fischer, Lanthanide phthalocyanine complexes, in: K.M. Kadish, K.M. Smith, R. Guilard (Eds.), The Porphyrin Handbook, vol. 16, Academic Press, NewYork, NY, 2003, pp. 171–246. A.T. Chang, J.C. Marchon, Preparation and characterization of oxidized and reduced forms of lutetium diphthalocyanine, Inorg. Chim. Acta 53 (1981) L241–L243. M. Bouvet, Radical phthalocyanines and intrinsic semiconduction, in: K.M. Kadish, K.M. Smith, R. Guilard (Eds.), Porphyrin Handbook, vol. 19, Academic Press, New York, NY, 2003, pp. 37–104. J.W. Buchler, D.K.P. Ng, Metal tetrapyrrole double- and triple-deckers with special emphasis on porphyrin systems, in: K.M. Kadish, K.M. Smith, R. Guilard (Eds.), Porphyrin Handbook, vol. 3, Academic Press, New York, NY; Burlington MA, 2000, pp. 245–294. K.M. Kadish, T. Nakanishi, A.G. Gurek, V. Ahsen, I. Yilmaz, Electrochemistry of a double-decker lutetium(III) phthalocyanine in aqueous media. The first evidence for five reductions, J. Phys. Chem. B 105 (2001) 9817–9821. M. Gonidec, E.S. Davies, J. McMaster, D.B. Amabilino, J. Veciana, Probing the magnetic properties of three interconvertible redox states of a single-Molecule magnet with magnetic circular dichroism spectroscopy, J. Am. Chem. Soc. 132 (2010) 1756–1757. N. Ishikawa, M. Sugita, T. Ishikawa, S. Koshihara, Y. Kaizu, Lanthanide double-Decker complexes functioning as magnets at the single-Molecular level, J. Am. Chem. Soc. 125 (2003) 8694–8695. K. Katoh, T. Komeda, M. Yamashita, The frontier of molecular spintronics based on multiple-Decker phthalocyaninato Tb III single-Molecule magnets, Chem. Rec. 16 (2016) 987–1016. C.H. Ziegler, J. Bufler, D. Martin, W. Göpel, Electronic structure and electrical properties of monomeric LuPc2 and polymeric (PcGaF)nphthalocyanines, Synth. Met. 55–57 (1993) 91–96. J. Simon, M. Bouvet, P. Bassoul, et al., The Encyclopedia of Advanced Materials, in: D. Bloor (Ed.), Pergamon Press, Oxford, 1994, p. 1680. M.L. Rodriguez-Méndez, Langmuir–Blodgett films of rare-earth lanthanide bisphthalocyanines: applications as sensors of gases and volatile organic compounds, Comm. Inorg. Chem. 22 (2000) 227–239. N. Gutierrez, M.L. Rodriguez-Méndez, J.A. de Saja, Array of sensors based on lanthanide bisphtahlocyanine Langmuir?Blodgett films for the detection of olive oil aroma, Sens. Actuators B 77 (2001) 437–442. J. Jiang, D.K.P. Ng, A decade journey in the chemistry of sandwich-type tetrapyrrolato-rare earth complexes, Acc. Chem. Res. 42 (2009) 79–88. J. Spadavecchia, G. Ciccarella, L. Valli, R. Rella, A novel multisensing optical approach based on a single phthalocyanine thin films to monitoring volatile organic compounds, Sens. Actuators B 113 (2006) 516–525. Yu. V. Burlachenko, B.A. Snopok, Multisensor arrays for gas analysis based on photosensitive organic materials: an increase in the discriminating capacity under selective illumination conditions, J. Anal.Chem. 63 (2008) 557–565. S. Shukla, R. Agrawal, H.J. Cho, S. Seal, L. Ludwig, C. Parish, Effect of UV radiation exposure on room temperature hydrogen sensitivity of nano-crystalline doped tin oxide sensor incorporated into microelectro mechanical system device, J. Appl. Phys. 97 (2005) 54307–54319. K.M. Mayer, J.H. Hafner, Localized surface plasmon resonance sensors, Chem. Rev. 111 (2011) 3828–3857. J.N. Anker, W. Paige Hall, O. Lyandres, N.C. Shah, J. Zhao, R.P. Van Duyne, Biosensing with plasmonic nanosensors, Nat. Mater. 7 (2008) 442–453. A.J. Haes, S. Zou, J. Zhao, G.C. Schatz, R.P. Van Duyne, Localized surface plasmon resonance spectroscopy near molecular resonances, J. Am. Chem. Soc. 128 (2006) 10905–10914. L. Malavolti, M. Mannini, P.-E. Car, G. Campo, F. Pineider, R. Sessoli, Erratic magnetic hysteresis of TbPc2 molecular nanomagnets, J. Mater. Chem. 1C (2013) 2935–2942. L. Margheriti, D. Chiappe, M. Mannini, P.E. Car, P. Sainctavit, M.A. Arrio, F.B. De Mongeot, J.C. Cezar, F.M. Piras, A. Magnani, E. Otero, A. Caneschi, R. Sessoli, X-Ray detected magnetic hysteresis of thermally evaporated terbium double-Decker oriented films, Adv. Mater. 22 (2010) 5488–5493. A. Hofmann, Z. Salman, M. Mannini, A. Amato, L. Malavolti, E. Morenzoni, T. Prokscha, R. Sessoli, A. Suter, Depth-Dependent spin dynamics in thin films of

274

[48]

[49]

[50]

[51]

[52]

[53]

[54]

[55] [56]

[57] [58]

A. Colombelli et al. / Sensors and Actuators B 253 (2017) 266–274 TbPc2 nanomagnets explored by low-Energy implanted muons, ACS Nano 6 (2012) 8390–8396. M.G. Manera, A. Colombelli, A. Taurino, M. Catalano, A. Convertino, R. Rella, Au nanoparticles decoration of silica nanowires for improved optical bio-sensing, Sens. Actuators B 226 (2016) 589–597. S. Heutz, S.M. Bayliss, R.L. Middleton, G. Rumbles, T.S. Jones, Polymorphism in phthalocyanine thin Films: Mechanism of the ␣ → ␤ transition, J. Phys. Chem. B 104 (2000) 7124–7129. S.M. Bayliss, S. Heutz, G. Rumbles, T.S. Jones, Thin fillm properties and surface morphology of metal free phthalocyanine grown by organic molecular beam deposition, Phys. Chem. Chem. Phys. 1 (1999) 3673–3676. D.D. Qi, L.J. Zhang, L. Wan, Y.X. Zhang, Y.Z. Bian, J.Z. Jiang, Conformational effects, molecular orbitals, and reaction activities of bis(phthalocyaninato) lanthanum double-deckers: density functional theory calculations, Phys. Chem. Chem. Phys. 13 (2011) 13277. S. Yu Elovich, G.M. Zhalrova, Mechanism of the catalytic hydrogenation of ethylene on nickel I. Kinetics of the process, Zh. Fiz. Khim. 13 (1939) 1761–1774. R. Rella, A. Serra, P. Siciliano, A. Tepore, L. Valli, A. Zocco, Langmuir-Blodgett multilayers based on copper phthalocyanine as gas sensor materials: active layer-gas interaction model and conductivity modulation, Langmuir 13 (1997) 6562–6567. A.J. Haes, S. Zou, J. Zhao, G.C. Schatz, R.P. Van Duyne, Localized surface plasmon resonance spectroscopy near molecular resonances, J. Am. Chem. Soc. 128 (2006) 10905–10914. ¨ Phys. Rev. B 73 (2006) T. Ambjornsson, G. Mukhopadhyay, S.P. Apell, M. Kall, (085421-1-10). J. Zhao, L. Jensen, J. Sung, S. Zou, G.C. Schatz, R.P. Van Duyne, Interaction of plasmon and molecular resonances for rhodamine 6G adsorbed on silver nanoparticles, J. Am. Chem. Soc. 129 (2007) 7647–7656. A.J. Wilson, K.A. Willets, Molecular plasmonics, Annu. Rev. Anal. Chem. 9 (2016) 27–43. G. Zengin, T. Gschneidtner, R. Verre, L. Shao, T.J. Antosiewicz, K. Moth-Poulsen, M. Kall, T. Shega, Evaluating conditions for strong coupling between nanoparticle plasmons and organic dyes using scattering and absorption spectroscopy, J. Phys. Chem. C 120 (2016) 20588–20596.

Biographies Adriano Colombelli obtained his degree in Physics in 2011 at the University of Salento in Lecce (Italy). In July 2015 he received a Ph.D. degree in Materials and Structural Engineering at the Innovation Engineering Department of the University of Salento, discussing a thesis on new strategies for modulation of nano-structured plasmonic materials. Since 2012 he joined as scholarship holder the Institute for Microelectronics and Microsystem of the National Research Council (CNR) in Lecce. He is involved in the development of chemical and biochemical sensors based on optical transduction mechanism. His research activities are focused on numerical simulation and experimental application of surface plasmon resonance based sensors, modeling and fabrication of micro-fluidics devices for medical applications. Matteo Mannini is a tenure track assistant professor at the Department of Chemistry of the University of Florence. He got his graduation in Chemistry cum laude with a thesis on the development of an OLED based on the Langmuir Blodgett technique in the Center for Colloids and Surface Science, University of Florence, then he moved to the Laboratory of Molecular Magnetism of the Department of Chemistry where he achieved in 2007 the PhD in Chemical Sciences and the European Doctorate in Molecular Magnetism with a thesis titled “Molecular Magnetic Materials on Solid Surfaces” awarded by the Italian Chemical Society. He has been early

stage researcher visitor at the Area Science Park, Trieste, Italy and at the Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), CNRS, France. He participated to several European and Italian research projects mainly focused on Molecular magnetism and Surface Science as an expert of the organization of single molecule magnets, organic radicals, redox isomers and spin cross-over on surfaces and their characterization using scanning probe microscopies and synchrotron based techniques. He is now interested in the evaluation of magnetic field effects in hybrid architectures and he is working on the incorporation of magnetic molecules and nanoparticles in these complex structures exploring their functional properties for photovoltaics, spintronic and magnetoplasmonic purposes. He received the “NEST award for Nanoscience” (2009) the “Niccolò Copernico award for Physics” (2010) and the “Raffaello Nasini Medal for Inorganic Chemistry” (2017). R. Rella, physicist, from 2001 senior researcher of the National Research Council at the Microelectronics and Microsystems Institute (IMM-CNR) unit of Lecce—Italy. Adjunct professor of material’s science and technology at the University of Salento. The research activity is connected with the optimization of prototypes of new devices for optoelectronic sensing and biosensing applications. Optics and optochemical sensors with new organic and inorganic material systems like metal oxide semiconductors, organic microcycles, conjugated polymers, dots and rods of metal oxide semiconductor, gold nanoparticles, organic/inorganic multilayer systems. Deposition in thin film form by using various preparation techniques, in particular self-assembly, spinning, thermal evaporation, self-assembly and Langmuir–Blodgett technique. The emphasis of this work is on the fabrication of electronic devices incorporating these layers in the realization of chemical (gas, vapor and liquid) sensors, self-organized structures and nanoscale devices. Analysis of the sensing performances and optimization of the sensing parameters. Development and application of surface-sensitive spectroscopic techniques such as surface plasmon resonance (SPR) imaging, magneto-plasmonic SPR, localized SPR. Chemical modification of metal surfaces for adsorption based biosensors (BIOMEMS). Michele Serri obtained his degree in Materials Science at the University of Pisa in 2009 and his diploma in Chemistry from Scuola Normale Superiore di Pisa in 2010. In 2014 he received a Ph.D. degree in Materials at the Imperial College of London, discussing a thesis on the magnetic properties of phthalocyanine thin films and nanomaterials. Then he moved to the Laboratory of Molecular magnetism at the University of Florence and the National Interuniversity Consortium of Materials Science and Technology (INSTM) where he applied magnetic force microscopy and synchrotron light spectroscopies to the study of thin films of molecular magnets. Since 2016 he joined the Graphene Lab at the Italian Institute of Technology in Genoa where he is developing printed optoelectronic devices based on 2D crystals. M.G. Manera is researcher of the National Research Council at the Microelectronics and Microsystems Institute (IMM-CNR) unit of Lecce—Italy. Her education degrees lie in the field of Physics and in particular Material Science and new applied technologies. Her research interests lie in the area of optical characterization of organic and inorganic materials for optochemical sensing and biosensing applications exploiting surface plasmon-based transduction methodologies both in the Propagating or Localized surfaces Plasmon modes. She has been involved also in the study and functional characterization of metal oxide based gas sensors, particularly when exposed to light illumination. Currently her interests are sweeping also in the functional characterization of magneto-plasmonic materials as novel magneto-optical transducing platforms for improving the gas and bio-sensing performances of standard surface plasmon resonance sensors. Novel research interests explored are in the area of plasmon-enhanced spectroscopies for materials science characterization and for functional devices development. She participated to several European and Italian research projects mainly focused on the same topics providing the coordination of some of them as a Principal Investigator.