Highly selective detection of l -Phenylalanine by molecularly imprinted polymers coated Au nanoparticles via surface-enhanced Raman scattering

Talanta 211 (2020) 120745

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Highly selective detection of L-Phenylalanine by molecularly imprinted polymers coated Au nanoparticles via surface-enhanced Raman scattering

T

Jiayuan Zhou, Sujitraj Sheth, Haifeng Zhou, Qijun Song∗ Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, Wuxi, 214122, PR China

ARTICLE INFO

ABSTRACT

Keywords: Molecularly imprinted polymers Surface-enhanced Raman scattering (SERS) AuNPs L-phenylalanine MIP-AuNPs sensor

Molecularly imprinted film coated gold nanoprticles (MIP-AuNPs) were employed as surface-enhanced Raman scattering (SERS) substrate for sensitive and selective recognition and quantification of L-Phenylalanine (L-Phe). The MIP was in-situ formed on the AuNPs by sol-gel technique using L-Phe as the template molecule, tetraethyl orthosilicate as the crosslinker and phenyltrimethoxysilane as the functional monomer. The efficient removal of template was achieved by ultrasonic treatment. The as-prepared MIP-AuNPs sensor showed a good linear relationship with the concentration of L-Phe in the range of 1.0 × 10−8–1.0 × 10−4 mol L−1 with a limit of detection as low as 1.0 nmol L−1. The sensor also showed an excellent selectivity as L-Phe can be determined in the presence of other amino acid analogues, D-Phe and bovine serum. The stability of the MIP-AuNPs was manifested by the low deviation (RSD = 3.7%) for 40 days subsequent measurements.

1. Introduction Surface-enhanced Raman scattering (SERS) has caught increasing attention for its wide detection scope ranging from chemical analysis, clinical analysis to environmental monitoring with high sensitivity [1–4]. According to the electromagnetic mechanism, noble metals are usually selected as SERS substrates, in which gold and silver are the most common. When target molecule does get absorbed or lie very close to the substrates, the Raman signals normally get enhanced [5]. However, bare noble metals are lacking specific binding sites, leading to the substrates respond to all molecules which possess Raman activity [6–11]. In order to realize the selective detection to particular target molecule, molecularly imprinted polymers (MIPs) have been combined with SERS [12,13]. MIPs, introducing “molecular memory” into the polymer, are thought of the most important tools for highly selective sensing [14–21]. By copolymerizing functional monomers and crosslinkers in the presence of the template molecule, MIPs are formed with 3D polymeric networks. After removing the template from networks, the specific recognition sites are remained, which exhibit high affinity to the template, whether in size, functionality or shape. Essentially, the recognition process is similar to enzyme-substrate or antigens-antibodies although there are some differences between them. MIPs are prepared by chemical synthesis method, so they have some advantages over the natural molecular recognition systems. In addition to its low

∗

cost, MIPs also exhibit higher performance in terms of stability and longer service life, which are manifested by the ability to resist harsh environmental conditions including the changes of pH and temperature in practical application [22–29]. Nowadays, MIPs have been combined with a variety of chemical technologies, such as Electrochemical [30], Electrogenerated chemiluminescence [31,32] and Fluorescence [33]. The combination of MIPs and SERS emphasizing for the detection of selective target has been reported in the literature [34–36]. MIP-SERS system usually be divided into two types as single and two steps based on the detection employed [37]. In two steps detection, the target molecule is extracted from complex samples by MIPs. Then the target molecule is eluted from MIPs and mixed with noble metals for SERS detection [38–40]. The single step detection is easy to operate and has advantages over two steps detection as it can directly introduce metal (Au or Ag) nanoparticles in MIP to form MIP-metal nanocomposite probe, which can separate and detect target molecule simultaneously [41–43]. This avoids loading, washing, elution and then detection comprising long analysis time and tedious operation, which are essential part for two steps detection. Only few reports employing MIP coated Au nanoparticles as a probe have been reported [42–45]. Besides, its applicability for detection of any amino acid has been rarely explored. Therefore there exist a huge task for analytical chemists to selectively detect amino acid by MIP coated Au nanoparticles as a single step assembled probe. L-Phenylalanine (L-Phe) is one of the eight essential amino acids,

Corresponding author. E-mail address: [email protected] (Q. Song).

https://doi.org/10.1016/j.talanta.2020.120745 Received 9 October 2019; Received in revised form 7 January 2020; Accepted 12 January 2020 Available online 13 January 2020 0039-9140/ © 2020 Elsevier B.V. All rights reserved.

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which is an indispensable nutrient required for normal people that cannot been synthesized by human [46]. The lack of L-Phe will lead to the depression and physical fatigue. So, people should obtain it from food. Also, people who take too much L-Phe can experience side effects such as headaches, nausea and heartburn [47]. In addition to it, patients with phenylketonuria (PKU) cannot digest L-Phe [48]. Thus, it is significant to control the intake of L-Phe. A sensitive method is needed urgently to detect L-Phe. At present, a lot of approaches have been developed, such as high-performance liquid chromatography (HPLC) [49], Electrogenerated Chemiluminescence [50], cell-based biosensor technology [51]. However, most of them obviously display drawbacks like time-consuming, complicated labor-intensive operation, complex instrumentation [52]. Therefore, it is still necessary to establish a highly selective and operationally easy method for L-Phe detection. In this work, we report the molecularly imprinted polymer coated gold nanoparticles (MIP-AuNPs) to selectively detect L-Phenylalanine (L-Phe) via single step approach. To the best of our knowledge, our developed MIP-AuNPs probe is the first to detect L-Phe via SERS method. The thickness of MIPs coated on the AuNPs was controlled strictly to obtain the best SERS signal. The sensitivity and selectivity of MIP-AuNPs to target molecule were investigated. The result indicated that the detectable concentration of L-Phe could be down to 1.0 nmol L−1 and MIP-AuNPs showed significantly higher selectivity to L-Phe than its analogues. Furthermore, the material was able to detect L-Phe quantitatively in real samples.

gel technology and molecule imprinting technique. Firstly, an amount of 2.5 mg L-Phe was added into 2.5 mL of solvent, a mixture consisting of ethanol and ultra-pure water (4:1, v/v), and dispersed by ultrasonication for 30 min. Secondly, 10 μL PTMOS was dropped into the mixed solution and then kept stirring for 6 h. Thirdly, 50 μL TEOS and 1 mL gold colloid were injected into the above solution. After that, the mixture was kept ultrasonication for 10 min. Finally, 50 μL HCl (0.1 M) was added and the resulting solution was vigorously stirred under room temperature for 24 h. The final products were collected by centrifugation (10000 rpm) then washed with ethanol and ultra-pure water for 3 times to remove the excessive reagents. The collected products were suspended in a mixed solvent of methanol and acetic acid (9:1, v/v) to remove the template. The washing process had to be operated for several times (1 h a time) until no template could be detected in the detergent by UV–Vis spectroscopy. The hybrids MIP-AuNPs were collected by centrifugation, then washed with ethanol and ultra-pure water in turn to get rid of the remaining acetic acid. Finally, MIP-AuNPs were dispersed into 800 μL ultra-pure water and stored at 4 °C before use. For comparison, non-imprinted polymers modified AuNPs (NIP-AuNPs) were synthesized with the same procedure, except the participation of template. 2.3. Preparation of bovine serum Bovine serum was bought from Kang Wei Century Biotechnology Co. Ltd. Before use, bovine serum was diluted 200 times with 0.01 M phosphate buffer saline solution (PBS) of pH 7.4 [54]. For deproteinization, 1.0 mL of bovine serum was mixed with 1.0 mL of 5-sulfosalicylic acid (2%, w/v) and kept shaking for 5 min. Then the homogenate was centrifuged and the supernatant was collected. Before analytical determination, the supernatant was diluted 100-fold with 0.01 M PBS (pH 7.4) [55].

2. Experimental 2.1. Materials and apparatus Tetraethyl orthosilicate (98%, TEOS) was bought from J & K Scientific. Chloroauric Acid Hydrate (HAuCl4·xH2O, 99%, Au: 50%), sodium citrate and phenyltrimethoxysilane (PTMOS) were purchase from Adamas Reagent Co., Ltd. L-Tryptophan (L-Try), L-Tyrosine (LTyr), L-Phenylalanine (L-Phe) and D-Phenylalanine (D-Phe) were bought from Sinopharm Chemical Reagent Co., Ltd. All the chemicals used in the experiment were all of analytical grade. Ultra-pure water (obtained from a Milli-Q water purifying system) was used in all processes throughout the experiment, including preparation and cleaning of materials. Transmission electron microscope (TEM, JEOL, JEM-2100 plus) was employed to characterize the morphology of samples, operated at the voltage of 200 KV. X-Ray diffraction spectrometer (XRD, D8, Bruker AXS, Germany) was used with Cu Kα radiation source over the 2θ range of 5–90°. The Raman spectra were recorded using the Microscopic confocal Raman spectrometer (inVia, Renishaw, England), and the excitation wavelength was set at 785 nm. The infrared spectra were recorded on a Fourier infrared spectrometer (Nicolet iS50 FT-IR, Thermo Fisher Scientific, USA).

3. Results and discussion 3.1. Preparation and characterization of MIP-AuNPs As illustrated in Fig. 1, the MIP-AuNPs were synthesized by the process of surface-initiated imprinted polymerization. Firstly, AuNPs were prepared by the method of sodium citrate reduction HAuCl4. Then MIPs were coated on the surface of AuNPs according to the sol-gel technique. Finally, the template molecules were eluted from MIPs. In order to improve the elution efficiency, the washing process was operated under ultrasonication. Heat generated by ultrasonic vibration of particles can also accelerate the elution of template molecules. The morphologies of synthesized AuNPs and MIP-AuNPs were investigated by TEM. Fig. 2 (a) shows the TEM image of AuNPs, which clearly illustrated the great dispersion and the average size was around 15 nm, by counting 50 particles as shown in Fig. 2 (a) inset. Compared to AuNPs, MIP-AuNPs shared the similar particle size, which could be found in Fig. 2 (b). Also, MIP-AuNPs revealed good dispersion after the long washing process. However, bare AuNPs were so sensitive to external factors that both long time ultrasonication and acidic environment would lead to aggregation. Thus, the obtained results indicated that the surface of AuNPs developed an ultra-thin protective film to prevent gold nanoparticles from the erosion by the external environment. Fig. 3 (a) showed the FT-IR spectra of MIP-AuNPs. It was clear that the materials exhibited a distinct peak at 1078 cm−1, ascribing to the vibration of Si–O, coming from TEOS and PTMOS [56,57]. There was a broad peak between 3690 and 3000 cm−1, belonging to the stretching vibration of O–H, produced by the hydrolysis of TEOS. In addition, the peak at 802 cm−1 could be ascribed to the symmetric vibration of Si–O–Si, which was the product of condensation reactions among hydrolysis of TEOS [58]. The band at 2935 cm−1 was corresponding to the stretching vibrations of C–H, which was an aliphatic C–H band. And

2.2. Preparation of MIPs coated AuNPs Prior to the synthesis, all of the glass apparatus were soaked in the aqua regia (HCl/HNO3, 3:1, v/v) for one day, after that rinsed with ultra-pure water and dried in the oven. The AuNPs were synthesized according to sodium citrate reduction of HAuCl4 method with some modifications [53]. Briefly, 1 mL of 1% (w/v) HAuCl4 solution was added into a round bottom flask, containing 99 mL ultra-pure water. The system was heated to boiling with continuous stirring, and then 3 mL of 1% (w/v) sodium citrate solution was rapidly added to the system. The mixture was then continuously boiled for 15 min after the appearance of stable wine-red color. The resultant solution was cooled down to room temperature and centrifuged. Finally, the precipitated AuNPs was re-dispersed in 10 mL ultra-pure water, termed as gold colloid and stored at 4 °C for subsequent use. The MIP-AuNPs hybrids were prepared by the combination of sol2

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Fig. 1. Illustration concerning the synthesis of the MIP-AuNPs and the SERS signal of MIP-AuNPs before and after the elution of L-Phe.

existence of AuNPs in the MIP-AuNPs. Summing up the conclusion of Fig. 3 (a) and Fig. 3 (b), MIPs and AuNPs are the components of MIP-AuNPs. In other words, the material of MIPs modified AuNPs was synthesized successfully. 3.2. Optimization of MIPs thickness coated on the AuNPs The electromagnetic field and plasmonic properties of AuNPs could be affected by the changes of nearby surroundings [59]. Therefore, it was of great importance to measure the distance between the template molecule and AuNPs. To obtain the best Raman signal enhancement, the template molecule needed to be in very close proximity to AuNPs, and the optimal distance should be less than one particle radius [44]. According to this theory, it was particularly important to control the thickness of MIPs coated on the AuNPs, which was the key influencing factor that affected the sensitivity of MIP-AuNPs towards SERS signal. In accordance with the process of experiment, the thickness of MIPs was controlled by TEOS and PTMOS. Hence, the effect of TEOS and PTMOS concentration on the SERS property of MIP-AuNPs before L-Phe extracted were studied [60–65]. During the process of investigating the optimal concentration of TEOS, 10 μL, 20 μL, 30 μL, 40 μL, 50 μL, 60 μL and 70 μL TEOS was added into systems separately while other experimental conditions were unchanged. The resultant products were analyzed by Raman spectroscopy and their Raman performance was shown in Fig. S1 in the supporting information. It could be found from the picture that the best amount of TEOS added was 50 μL. The same procedure was carried out to study the most appropriate PTMOS concentration and according to the result recorded in Fig. S2, the optimal amount of PTMOS added was

Fig. 2. The TEM images of AuNPs (a), and MIP-AuNPs (b), also exhibiting the size distribution of AuNPs diameter by counting 50 particles (inset a).

the other peaks around 1623 cm−1 and 960 cm−1 resulted from the vibration of C]C, and the out-of-plane deformation vibration of = C–H respectively. However, there was no peak around 3020-3000 cm−1, maybe due to the existence of the stretching vibration of O–H in this range, which was too wide to show the stretching vibration of = C–H on aromatic hydrocarbons. According to the observed IR bands, the presence of MIPs in the MIP-AuNPs could be confirmed. The crystalline phase of MIP-AuNPs was characterized by XRD with the 2θ range of 30–90° as shown in Fig. 3 (b). The XRD spectra showed five diffraction peaks, locating at 2θ = 38.10°, 44.369°, 64.677°, 77.547°, and 81.503° respectively, indexed to the typical face-centered cubic of AuNPs. According to JCPDS card (No. 02–1095), the five diffraction peaks were well matched with the crystal phase of (111), (200), (220), (311), and (222). This directly gave an indication of the

Fig. 3. The FT-IR spectra of MIP-AuNPs (a) and the XRD patterns of MIP-AuNPs (b). 3

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10 μL. Therefore, under optimized conditions, the L-Phe can be automatically captured by the molecular imprinting layer to maintain an optimal distance from gold nanoparticles with electromagnetic field and plasma effect, thereby ensuring a high sensitivity of the SERS sensor. 3.3. Selectivity of the MIP-AuNPs NIP-AuNPs and L-Phe solid were used to investigate the Raman performance of MIP-AuNPs before L-Phe was extracted. As shown in Fig. S3, a distinct peak around 1000 cm−1 could be found in the Raman spectrum of L-Phe solid, which was selected as the characteristic peak to analyze sensitivity and selectivity of the MIP-AuNPs. As expected, the Raman signal of MIP-AuNPs matched well with L-Phe solid. Compared to L-Phe solid and MIP-AuNPs, there was almost no peak in Raman spectrum of NIP-AuNPs. Although this conclusion has been foreseen, it was even more powerful evidence that the constructed molecularly imprinted membrane layer could capture the target molecules well, showing excellent ability to recognize and quantify. Furthermore, it was necessary to study the selectivity of MIP-AuNPs, on account of the complexity of actual samples. D-Phe, L-Try and L-Tyr were selected as the analogues, since their structural analogy with LPhe. The study was carried out by incubating MIP-AuNPs with 1 μM LPhe, 10 μM D-Phe, 10 μM L-Try, 10 μM L-Tyr and NIP-AuNPs were incubated with L-Phe, D-Phe, L-Try, L-Tyr at the concentration of 10 μM. As shown in Fig. 4 (a), due to the presence of the specific recognition sites providing particular channel for L-Phe approaching to AuNPs surface and functional group to interact with L-Phe, MIP-AuNPs exhibited higher Raman signal to L-Phe than its analogues at the peak around 1000 cm−1 and even its chiral isomer D-Phe was no exception. However, NIP-AuNPs showed similar sensitivity to all analytes, indicating that the Raman signals originated from the nonspecific adsorption of analytes on NIP-AuNPs surfaces. The results indicated that the customizable molecularly imprinted channel of MIP-AuNPs had a unique affinity for capturing L-Phe with high selectivity, which had a more unique advantage in complex samples. The selectivity of MIP-AuNPs was further studied by comparing the Raman performance of L-Phe in the presence of D-Phe, L-Try and L-Tyr with various concentration ratios (L-Phe/D-Phe/L-Try/L-Tyr = 1:0:0:0, 1:1:1:1 and 1:10:10:10). In this process, the concentration of L-Phe was controlled at 2.5 × 10−7 mol L−1. According to the result shown in Fig. 4 (b), the intensity of SERS signal at 1000 cm−1 was increased 2.4% and 5.2% respectively in the one-fold and ten-fold excess of DPhe, L-Try and L-Tyr, compared to the bare L-Phe condition. Thus, the obtained results further confirmed the fact that the excellent recognition ability of MIP-AuNPs showed high selectivity even for enantiomers with similar structures, which opened the way for the development of highly sensitive chiral sensing platforms.

Fig. 4. Raman spectra of MIP-AuNPs incubated with 1.0 × 10−6 mol L−1 LPhe, 1.0 × 10−5 mol L−1 D-Phe, 1.0 × 10−5 mol L−1 L-Try, 1.0 × 10−5 mol L−1 L-Tyr and NIP-AuNPs incubated with L-Phe, D-Phe, L-Try, L-Tyr at the concentration of 1.0 × 10−5 mol L−1 (a); Raman performance of MIP-AuNPs in the presence of L-Phe, D-Phe, L-Try and L-Tyr with various concentration ratios (L-Phe/D-Phe/L-Try/L-Tyr = 1:0:0:0, 1:1:1:1 and 1:10:10:10) and the concentration of L-Phe controlled at 2.5 × 10−7 mol L−1 (b).

belonging to the bare AuNPs (blue line). After incubated with 1.0 × 10−8 mol L-1 L-Phe (red line), there was no tendency of strengthening in the Raman signals, indicating that the concentration of 1.0 × 10−8 mol L−1 was out of detection range of AuNPs. The phenomena above also explained why the Raman signal of MIP-AuNPs incubated with blank solution [Fig. 5 (a) black line] was not a straight line. And the peak was so weak that had few influence on the L-Phe detection. Fig. S4 reflected that the detection limit of AuNPs to L-Phe was 100 nM. Apart from that, distinct Raman signal could be found in the Raman spectrum of MIP-AuNPs incubated with 1.0 × 10−8 mol L−1 L-Phe. Thanks to the contribution of MIPs coated on the AuNPs, which had the specific recognition sites and exhibited high affinity to L-Phe, leading to more L-Phe absorbed to the sites. However, when AuNPs and MIP-AuNPs were incubated with 1.0 × 10−3 mol L−1 L-Phe, MIPAuNPs did not show any superiority in Raman context. As shown in Fig. 5 (d), AuNPs exhibited higher Raman intensity than MIP-AuNPs. In that case, the enrichment effect of MIPs was disappearing, on account of sufficient L-Phe existing in the solution and compared to MIP-AuNPs, AuNPs possessing more binding sites. In summary, MIP-AuNPs had advantages on low concentration detection to L-Phe. In other words, MIP-AuNPs exhibited higher sensitivity in the detection of L-Phe than AuNPs.

3.4. Sensitivity of the MIP-AuNPs Prior to Raman spectra used to analyze sensitivity of the MIPAuNPs, the hybrids were incubated with different concentration of LPhe solutions for 1 h. As shown in Fig. 5 (a), the peak intensity around 1000 cm−1 increased with the increasing concentration of L-Phe. Initially, the Raman intensity was very weak and there was no enough distinction compared to the blank when the concentration of L-Phe was lower than 1.0 nmol L−1. Hence, the detection limit of L-Phe using MIPAuNPs based SERS method can be estimated as 1.0 nmol L−1. In Fig. 5 (b), there was a good linear relationship in the range of L-Phe concentration between 1.0 × 10−4 and 1.0 × 10−8 mol L−1, and the coefficient of determination (R2) was 0.975. To compare the performance of AuNPs and MIP-AuNPs on the detection of L-Phe, AuNPs and MIP-AuNPs were dispersed into L-Phe solution for 1 h and then studied by Raman spectroscopy. The result was reflected in Fig. 5 (c). There was a weak signal around 1000 cm−1 4

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Fig. 5. Raman spectra of MIP-AuNPs incubated with L-Phe solution at the concentration of 0 mol L−1, 1.0 × 10−3 mol L−1, 1.0 × 10−4 mol L−1, 1.0 × 10−5 mol L−1, 1.0 × 10−6 mol L−1, 1.0 × 10−7 mol L−1, 1.0 × 10−8 mol L−1, 1.0 × 10−9 mol L−1 (a), Raman intensity of L-Phe solution with different concentration at 1000 cm−1 detected by MIP-AuNPs and the inset showing a good linear relationship in the range of 1.0 × 10−41.0 × 10−8 mol L−1 (b), Raman spectra of MIPAuNPs and AuNPs incubated with 1.0 × 10−8 mol L−1 L-Phe solution, the blank representing Raman signal of bare AuNPs (c), Raman spectra of MIP-AuNPs and AuNPs incubated with 1.0 × 10−3 mol L−1 L-Phe solution (d).

Table 1 Determination of L-Phe in spiked bovine serum samples. Samples

Spiked (10 μM)

Found (10 μM)

Recovery (%)

1 2 3 4* 5* 6*

5 10 20 5 10 26

4.97 10.39 19.05 4.93 9.67 20.81

99.40 103.90 95.25 98.6 96.7 104.1

* The samples after protein removed.

incubated with L-Phe standard solution and the rest MIP-AuNPs were stored in the refrigerator at 4 °C for later use. The Follow-up tests were scheduled for 10 days, 20 days, 30 days and 40 days, respectively. As shown in Fig. 6 (a), there were slight fluctuations in the values between original and others detected in the later experiment. The relative standard deviation (RSD) was 3.7%, indicating the good stability of MIP-AuNPs. In the case of study the repeatability of SERS signal, template molecule was extracted from MIP-AuNPs by methanol-acetic acid solution for five times. From Fig. 6 (b), we could find the decline trend of SERS intensity, which was caused by the damage to the specific recognition sites during elution process. Even so, the decline trend was not obvious. In the second cycle, the SERS intensity maintained 97% of the original value. After the third cycle, the original SERS intensity still kept 92%. When five cycles passed, the SERS intensity just decreased about 27% compared to the original value. In general, MIP-AuNPs exhibited excellent stability and reusability. Fig. 6. The stable (a), and repetitive (b) performance of MIP-AuNPs (L-Phe concentration, 1.0 × 10−5 mol L−1).

3.6. Application for analysis in real sample The analysis of the practical application of MIP-AuNPs was examined in bovine serum. In this study, calculated amounts of L-Phe were added in the diluted bovine serum samples, respectively and the result was listed in Table 1. Recovery was measured and lied in the range of 95.25–103.9%. To figure out whether the protein in bovine serum would have effect on the result, the same procedure was operated in the deproteinized bovine serum samples. As shown in Table 1,

3.5. Stability and reusability of MIP-AuNPs The stability and reusability of MIP-AuNPs were studied by monitoring SERS intensity changes of the band at 1000 cm−1 and the concentration of L-Phe was controlled at 1.0 × 10−5 mol L−1. To investigate the stability, some of the freshly prepared MIP-AuNPs were 5

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Table 2 Comparison of this method we proposed with others reported in the literature. Methods High-Performance Liquid Chromatography Electrogenerated Chemiluminescence cell-based biosensor technology MIP-SERS

linear range −6

−3

6.0 × 10 -1.51 × 10 M 6.05 × 10−7-3.0 × 10−4 M −6 −4 M 5.0 × 10 -1.0 × 10 1.0 × 10−8-1.0 × 10−4 M

the recovery was distributed in the range of 96.7–104.1%, indicating that the protein in bovine serum had no effect on results. Table 2 displayed the comparison between methods reported in the literature and our method for the detection of L-Phe. It can be seen that our method exhibited competitive sensitivity and a wider linear range.

detection limit

Reference

1.5 μM 0.16 μM 3.7 μM 1 nM

[49] [50] [51] This work

[10] M.R. Awual, Novel nanocomposite materials for efficient and selective mercury ions capturing from wastewater, Chem. Eng. J. 307 (2017) 456–465. [11] M.R. Awual, N.H. Alharthi, M.M. Hasan, M.R. Karim, A. Islam, H. Znad, Inorganicorganic based novel nano-conjugate material for effective cobalt(II) ions capturing from wastewater, Chem. Eng. J. 324 (2017) 130–139. [12] S.N. Chen, X. Li, S. Han, J.H. Liu, Y.Y. Zhao, Synthesis of surface-imprinted Ag nanoplates for detecting organic pollutants in water environments based on surface enhanced Raman scattering, RSC Adv. 5 (2015) 99914–99919. [13] A.A. Volkert, A.J. Haes, Advancements in nanosensors using plastic antibodies, Analyst 139 (2014) 21–31. [14] J.J. BelBruno, Molecularly imprinted polymers, Chem. Rev. 119 (2019) 94–119. [15] M. Gast, S. Kuhner, H. Sobek, P. Walther, B. Mizaikoff, Enhanced selectivity by passivation: molecular imprints for viruses with exceptional binding properties, Anal. Chem. 90 (2018) 5576–5585. [16] S. Saglam, A. Uzer, E. Ercag, R. Apak, Electrochemical determination of TNT, DNT, RDX, and HMX with gold nanoparticles/poly(carbazole-aniline) film-modified glassy carbon sensor electrodes imprinted for molecular recognition of nitroaromatics and nitramines, Anal. Chem. 90 (2018) 7364–7370. [17] R. Xing, S. Wang, Z. Bie, H. He, Z. Liu, Preparation of molecularly imprinted polymers specific to glycoproteins, glycans and monosaccharides via boronate affinity controllable-oriented surface imprinting, Nat. Protoc. 12 (2017) 964–987. [18] Z. Zhang, X. Zhang, B. Liu, J. Liu, Molecular imprinting on inorganic nanozymes for hundred-fold enzyme specificity, J. Am. Chem. Soc. 139 (2017) 5412–5419. [19] R. Yu, H. Zhou, M. Li, Q. Song, Rational selection of the monomer for molecularly imprinted polymer preparation for selective and sensitive detection of 3-methylindole in water, J. Electroanal. Chem. 832 (2019) 129–136. [20] M.L. Yola, N. Atar, Electrochemical detection of atrazine by platinum nanoparticles/carbon nitride nanotubes with molecularly imprinted polymer, Ind. Eng. Chem. Res. 56 (2017) 7631–7639. [21] X. Ying, H.-T. Yoshioka, C. Liu, F. Sassa, K. Hayashi, Molecular imprinting technique in putrescine visualized detection, Sens. Actuators B Chem. 258 (2018) 870–880. [22] M.R. Awual, Mesoporous composite material for efficient lead(II) detection and removal from aqueous media, J. Environ. Chem. Eng. 7 (2019) 103124. [23] M.R. Awual, A facile composite material for enhanced cadmium(II) ion capturing from wastewater, J. Environ. Chem. Eng. 7 (2019) 103378. [24] M.R. Awual, Novel conjugated hybrid material for efficient lead(II) capturing from contaminated wastewater, Mater. Sci. Eng. C 101 (2019) 686–695. [25] M.R. Awual, Novel ligand functionalized composite material for efficient copper(II) capturing from wastewater sample, Compos. B Eng. 172 (2019) 387–396. [26] M.R. Awual, T. Yaita, S.A. El-Safty, H. Shiwaku, S. Suzuki, Y. Okamoto, Copper(II) ions capturing from water using ligand modified a new type mesoporous adsorbent, Chem. Eng. J. 221 (2013) 322–330. [27] M.R. Awual, M. Ismael, T. Yaita, S.A. El-Safty, H. Shiwaku, Y. Okamoto, Trace copper(II) ions detection and removal from water using novel ligand modified composite adsorbent, Chem. Eng. J. 222 (2013) 67–76. [28] M.R. Awual, M.M. Hasan, A. Shahat, M. Naushad, H. Shiwaku, T. Yaita, Investigation of ligand immobilized nano-composite adsorbent for efficient cerium (III) detection and recovery, Chem. Eng. J. 265 (2015) 210–218. [29] M.R. Awual, M.M. Hasan, M.A. Khaleque, M.C. Sheikh, Treatment of copper(II) containing wastewater by a newly developed ligand based facial conjugate materials, Chem. Eng. J. 288 (2016) 368–376. [30] N. Ermiş, L. Uzun, A. Denizli, Preparation of molecularly imprinted electrochemical sensor for l-phenylalanine detection and its application, J. Electroanal. Chem. 807 (2017) 244–252. [31] J. Cai, T. Chen, Y. Xu, S. Wei, W. Huang, R. Liu, A versatile signal-enhanced ECL sensing platform based on molecular imprinting technique via PET-RAFT crosslinking polymerization using bifunctional ruthenium complex as both catalyst and sensing probes, Biosens. Bioelectron. 124–125 (2019) 15–24. [32] N. Cao, P. Zeng, F. Zhao, B. Zeng, Fabrication of molecularly imprinted polypyrrole/Ru@ethyl-SiO2 nanocomposite for the ultrasensitive electrochemiluminescence sensing of 17β-Estradiol, Electrochim. Acta 291 (2018) 18–23. [33] L. Xu, M. Pan, G. Fang, S. Wang, Carbon dots embedded metal-organic framework@ molecularly imprinted nanoparticles for highly sensitive and selective detection of quercetin, Sens. Actuators B Chem. 286 (2019) 321–327. [34] K. Kantarovich, I. Tsarfati, L.A. Gheber, K. Haupt, I. Bar, Writing droplets of molecularly imprinted polymers by nano fountain pen and detecting their molecular interactions by surface-enhanced Raman scattering, Anal. Chem. 81 (2009) 5686–5690. [35] K. Kantarovich, I. Tsarfati, L.A. Gheber, K. Haupt, I. Bar, Reading microdots of a molecularly imprinted polymer by surface-enhanced Raman spectroscopy, Biosens. Bioelectron. 26 (2010) 809–814. [36] J. Wackerlig, P.A. Lieberzeit, Molecularly imprinted polymer nanoparticles in chemical sensing – synthesis, characterisation and application, Sens. Actuators B

4. Conclusions We have developed an efficient method to detect L-Phe with sensitivity and selectivity. MIP-AuNPs, served as a SERS substrate, was synthesized by sol-gel technology and surface imprinting technique. The ultra-thin MIP film, coated on the AuNPs, provided specific binding sites for L-Phe. The specific binding sites played very important role in realizing the selective detection of target molecules by preventing interferents from getting in touch with AuNPs. And the detection limit of L-Phe, combined with MIP-AuNPs was as low as 1.0 nmol L−1. The intensity of SERS signal at 1000 cm−1 showed a good linear relationship with the concentration of L-Phe on MIP-AuNPs in the range of 1.0 × 10−4-1.0 × 10−8 mol L−1. Moreover, MIP-AuNPs had wonderful performance in the detection of L-Phe in real samples. In general, the developed method was a sensitive and effective method to detect L-Phe and could be used in more practical applications with tremendous potential value. Acknowledgements This work is supported by the National First-Class Discipline Program of Food Science and Technology (JUFSTR20180301), the Fundamental Research Funds for the Central Universities (No. JUSRP11708), and the 111 Project (B13025). Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.talanta.2020.120745. References [1] J. Cui, K. Hu, J.J. Sun, L.L. Qu, D.W. Li, SERS nanoprobes for the monitoring of endogenous nitric oxide in living cells, biosens, Bioelectron 85 (2016) 324–330. [2] Y.-H. Lai, S.-W. Chen, M. Hayashi, Y.-J. Shiu, C.-C. Huang, W.-T. Chuang, Mesostructured arrays of nanometer-spaced gold nanoparticles for ultrahigh number density of SERS hot spots, Adv. Funct. Mater. 24 (2014) 2544–2552. [3] Y. Zhang, S. Zhao, J. Zheng, L. He, Surface-enhanced Raman spectroscopy (SERS) combined techniques for high-performance detection and characterization, Trends Anal. Chem. 90 (2017) 1–13. [4] H. Zhang, L. Sun, Y. Zhang, Y. Kang, H. Hu, H. Tang, Production of stable and sensitive SERS substrate based on commercialized porous material of silanized support, Talanta 174 (2017) 301–306. [5] T. Koker, N. Tang, C. Tian, W. Zhang, X. Wang, R. Martel, Cellular imaging by targeted assembly of hot-spot SERS and photoacoustic nanoprobes using splitfluorescent protein scaffolds, Nat. Commun. 9 (2018) 607–623. [6] M.R. Awual, Innovative composite material for efficient and highly selective Pb(II) ion capturing from wastewater, J. Mol. Liq. 284 (2019) 502–510. [7] M.R. Awual, M.M. Hasan, G.E. Eldesoky, M.A. Khaleque, M.M. Rahman, M. Naushad, Facile mercury detection and removal from aqueous media involving ligand impregnated conjugate nanomaterials, Chem. Eng. J. 290 (2016) 243–251. [8] M.R. Awual, Solid phase sensitive palladium(II) ions detection and recovery using ligand based efficient conjugate nanomaterials, Chem. Eng. J. 300 (2016) 264–272. [9] M.R. Awual, New type mesoporous conjugate material for selective optical copper (II) ions monitoring & removal from polluted waters, Chem. Eng. J. 307 (2017) 85–94.

6

Talanta 211 (2020) 120745

J. Zhou, et al. Chem. 207 (2015) 144–157. [37] R. Hu, R. Tang, J. Xu, F. Lu, Chemical nanosensors based on molecularly-imprinted polymers doped with silver nanoparticles for the rapid detection of caffeine in wastewater, Anal. Chim. Acta 1034 (2018) 176–183. [38] X. Cao, F. Zhao, Z. Jiang, S. Hong, C. Zhang, Y. She, Rapid analysis of bitertanol in agro-products using molecularly imprinted polymers-surface-enhanced Raman spectroscopy, Food Anal. Method 11 (2017) 1435–1443. [39] F. Gao, E. Grant, X. Lu, Determination of histamine in canned tuna by molecularly imprinted polymers-surface enhanced Raman spectroscopy, Anal. Chim. Acta 901 (2015) 68–75. [40] T. Kamra, T. Zhou, L. Montelius, J. Schnadt, L. Ye, Implementation of molecularly imprinted polymer beads for surface enhanced Raman detection, Anal. Chem. 87 (2015) 5056–5061. [41] X. Ren, E.C. Cheshari, J. Qi, X. Li, Silver microspheres coated with a molecularly imprinted polymer as a SERS substrate for sensitive detection of bisphenol A, Microchim. Acta 185 (2018) 242–249. [42] T. Shahar, T. Sicron, D. Mandler, Nanosphere molecularly imprinted polymers doped with gold nanoparticles for high selectivity molecular sensors, Nano Res. 10 (2017) 1056–1063. [43] J.Q. Xue, D.W. Li, L.L. Qu, Y.T. Long, Surface-imprinted core-shell Au nanoparticles for selective detection of bisphenol A based on surface-enhanced Raman scattering, Anal. Chim. Acta 777 (2013) 57–62. [44] M. Bompart, Y. De Wilde, K. Haupt, Chemical nanosensors based on composite molecularly imprinted polymer particles and surface-enhanced Raman scattering, Adv. Mater. 22 (2010) 2343–2348. [45] S. Carrasco, E. Benito-Peña, F. Navarro-Villoslada, J. Langer, M.N. Sanz-Ortiz, J. Reguera, Multibranched gold–mesoporous silica nanoparticles coated with a molecularly imprinted polymer for label-free antibiotic surface-enhanced Raman scattering analysis, Chem. Mater. 28 (2016) 7947–7954. [46] H. Yang, L. Chen, C. Zhou, X. Yu, A.E.A. Yagoub, H. Ma, Improving the extraction of l-phenylalanine by the use of ionic liquids as adjuvants in aqueous biphasic systems, Food Chem. 245 (2018) 346–352. [47] R. Mahalakshmi, S.X. Jesuraja, S.J. Das, Growth and characterization of L-phenylalanine, Cryst. Res. Technol. 41 (2006) 780–783. [48] V. Singh, R.K. Rai, A. Arora, N. Sinha, A.K. Thakur, Therapeutic implication of Lphenylalanine aggregation mechanism and its modulation by D-phenylalanine in phenylketonuria, Sci. Rep. 4 (2014) 3875. [49] X.M. Mo, Y. Li, A.G. Tang, Y.P. Ren, Simultaneous determination of phenylalanine and tyrosine in peripheral capillary blood by HPLC with ultraviolet detection, Clin. Biochem. 46 (2013) 1074–1078. [50] J. Lu, S. Ge, F. Wan, J. Yu, Detection of L-phenylalanine using molecularly imprinted solid-phase extraction and flow injection electrochemiluminescence, J. Sep. Sci. 35 (2012) 320–326. [51] C. Lin, Y.C. Jair, Y.C. Chou, P.S. Chen, Y.C. Yeh, Transcription factor-based

[52] [53] [54]

[55] [56] [57]

[58] [59] [60] [61] [62] [63] [64] [65]

7

biosensor for detection of phenylalanine and tyrosine in urine for diagnosis of phenylketonuria, Anal. Chim. Acta 1041 (2018) 108–113. S.A. Zaidi, Facile and efficient electrochemical enantiomer recognition of phenylalanine using β-Cyclodextrin immobilized on reduced graphene oxide, Biosens. Bioelectron. 94 (2017) 714–718. X. Zhang, H. Zhao, Y. Xue, Z. Wu, Y. Zhang, Y. He, Colorimetric sensing of clenbuterol using gold nanoparticles in the presence of melamine, Biosens. Bioelectron. 34 (2012) 112–117. E. Martínez-Periñán, E. Sánchez-Tirado, A. González-Cortés, R. Barderas, J.M. Sánchez-Puelles, L. Martínez-Santamaría, Amperometric determination of endoglin in human serum using disposable immunosensors constructed with poly (pyrrolepropionic) acid-modified electrodes, Electrochim. Acta 292 (2018) 887–894. Y. Zhang, R.H. Yang, F. Liu, K.A. Li, Fluorescent sensor for imidazole derivatives based on Monomer?Dimer equilibrium of a zinc porphyrin complex in a polymeric film, Anal. Chem. 76 (2004) 7336–7345. T. Gan, J. Li, A. Zhao, J. Xu, D. Zheng, H. Wang, Detection of theophylline using molecularly imprinted mesoporous silica spheres, Food Chem. 268 (2018) 1–8. J. Huang, Y. Wu, J. Cong, J. Luo, X. Liu, Selective and sensitive glycoprotein detection via a biomimetic electrochemical sensor based on surface molecular imprinting and boronate-modified reduced graphene oxide, Sens. Actuators B Chem. 259 (2018) 1–9. H. Li, X. Wang, Z. Wang, Y. Wang, J. Dai, L. Gao, A polydopamine-based molecularly imprinted polymer on nanoparticles of type SiO2@rGO@Ag for the detection of lambda-cyhalothrin via SERS, Microchim. Acta 185 (2018) 193–202. I.M.A. Otto, H. Grabhorn, W. Akemann, Surface-enhanced Raman scattering, J. Phys. Condens. Matter 4 (1992) 1143–1212. M.R. Awual, Efficient phosphate removal from water for controlling eutrophication using novel composite adsorbent, J. Clean. Prod. 228 (2019) 1311–1319. M.R. Awual, S. Suzuki, T. Taguchi, H. Shiwaku, Y. Okamoto, T. Yaita, Radioactive cesium removal from nuclear wastewater by novel inorganic and conjugate adsorbents, Chem. Eng. J. 242 (2014) 127–135. M.R. Awual, T. Yaita, T. Taguchi, H. Shiwaku, S. Suzuki, Y. Okamoto, Selective cesium removal from radioactive liquid waste by crown ether immobilized new class conjugate adsorbent, J. Hazard Mater. 278 (2014) 227–235. M.R. Awual, Y. Miyazaki, T. Taguchi, H. Shiwaku, T. Yaita, Encapsulation of cesium from contaminated water with highly selective facial organic–inorganic mesoporous hybrid adsorbent, Chem. Eng. J. 291 (2016) 128–137. M.R. Awual, Ring size dependent crown ether based mesoporous adsorbent for high cesium adsorption from wastewater, Chem. Eng. J. 303 (2016) 539–546. M.R. Awual, N.H. Alharthi, Y. Okamoto, M.R. Karim, M.E. Halim, M.M. Hasan, Ligand field effect for Dysprosium(III) and Lutetium(III) adsorption and EXAFS coordination with novel composite nanomaterials, Chem. Eng. J. 320 (2017) 427–435.