A dichromatic label-free aptasensor for sulfadimethoxine detection in fish and water based on AuNPs color and fluorescent dyeing of double-stranded DNA with SYBR Green I
A dichromatic label-free aptasensor for sulfadimethoxine detection in fish and water based on AuNPs color and fluorescent dyeing of double-stranded DNA with SYBR Green I
Journal Pre-proofs A dichromatic label-free aptasensor for sulfadimethoxine detection in fish and water based on AuNPs color and fluorescent dyeing of...
Journal Pre-proofs A dichromatic label-free aptasensor for sulfadimethoxine detection in fish and water based on AuNPs color and fluorescent dyeing of double-stranded DNA with SYBR Green I Xiang-Xiu Chen, Zheng-Zhong Lin, Cheng-Yi Hong, Qiu-Hong Yao, Zhi-Yong Huang PII: DOI: Reference:
Please cite this article as: Chen, X-X., Lin, Z-Z., Hong, C-Y., Yao, Q-H., Huang, Z-Y., A dichromatic label-free aptasensor for sulfadimethoxine detection in fish and water based on AuNPs color and fluorescent dyeing of doublestranded DNA with SYBR Green I, Food Chemistry (2019), doi: https://doi.org/10.1016/j.foodchem.2019.125712
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A dichromatic label-free aptasensor for sulfadimethoxine detection in fish and water based on AuNPs color and fluorescent dyeing of double-stranded DNA with SYBR Green I Xiang-Xiu Chen1, Zheng-Zhong Lin1, Cheng-Yi Hong1, Qiu-Hong Yao3, Zhi-Yong Huang1,2
†
1. College of Food and Biological Engineering, Jimei University, Xiamen, 361021, China 2. Fujian Collaborative Innovation Center for Exploitation and Utilization of Marine Biological Resources, Xiamen, 361102, China 3. Xiamen Huaxia University, Xiamen, 361021, China Abstract:
A dichromatic label-free aptasensor was described for sulfadimethoxine (SDM) detection. Compared with the binding of SDM-aptamer to SDM, the higher affinity of aptamer to cDNA may result in the hybridization of dsDNA. In the presence of SDM, the aptamer specifically binds to SDM, leading to a blue color of AuNPs in deposit and fluorescence at 530 nm in supernatant after adding cDNA and SGI. With no target of SDM, AuNPs protected with the aptamer re-disperse in PBS with a red color, and no fluorescence occurs in supernatant. Based on the principle, SDM can be quantitatively detected through both fluorescent emission and AuNPs color changes with recoveries ranging from 99.2% to 102.0% for fish and from 99.5% to 100.5% for water samples. An analytical linear range of 2-300 ng mL-1 was achieved with a detection limits of 3.41 ng mL-1 for water and 4.41 ng g-1 for fish samples (3σ, n=9). Keywords: Aptasensor; gold nanoparticles; fluorescence; sulfadimethoxine; water; fish
Sulfonamides are commonly used as antibacterial agents for the treatment of bacterial infections in aquaculture (Chokejaroenrat, Sakulthaew, Angkaew, Satapanajaru, Poapolathep, & Chirasatienpon, 2019). Sulfadimethoxine (SDM) is a sulfonamide that can be detected most frequently in water and fish samples (Gaffney, Almeid, Rodrigues, Ferreira, Benoliel, & Cardoso, 2015; Yuan, Qiang, Ben, Zhu, & Qu, 2015) and in fresh milk/dairy products (Beltr á n, Berruga, Molina, Althaus, & Molina, 2015; Chiesa, et al, 2012; Furusawa, 2000). The intake of SDM through food chain may present toxic reactions, superinfection and drug resistance for human health (Bia łk-Bielińska et al., 2012). Therefore, European Commission (EC) and China have proposed a maximum residue limit (MRL) of SDM 100 ng mL-1 in foodstuffs (Wang, Zhao, Chen, Tan, Zhang, & Quan, 2017). High performance liquid chromatography (HPLC) (Mahmoud, Khaleel, Hadad, Abdel-Salam, Haiß, & K ümmerer, 2013), capillary electrophoresis (CE) (Castro-Puyana, Crego, & Marina, 2008), and enzyme-linked immunosorbent assay (ELISA) (Muldoon, Buckley, Deshpande, Holtzapple, Beler, & Stanker, 2000) and immunochromatographic lateral flow strip test (Chen, Guo, Liu, Song, Kuang, & Xu, 2017) are the routine detection methods for SDM residue. These methods have low limits of detection (LODs) meeting the requirement of MRL, but have some shortcomings, including time-consuming, expensive instruments and complicate operation procedures (Ma, Wang, Jia, & Xiang, 2018; Yang et al, 2017). Therefore, it is urgent to develop an economical, portable, and high-throughput method to detect SDM residue sensitively and specifically. Aptamers are single-stranded DNA/RNA (ssDNA/RNA) oligonucleotides that possess the advantages of simple synthesis, easy and controllable modification, and long-term stability (Chen, Li, Tu, & Luo, 2018). Aptamers have high affinity and specificity with a wide range of targets (Wang et al, 2017; Sun, Tan, & Zu, 2016; Yang, Yin, Li, Lu, Zhang, & Sun, 2017). Since DNA-aptamer against SDM was screened by Song et al. in 2012 (Song, Jeong, Jeon, Jo, & Ban, 2
2012), the aptamer has been employed to detect SDM in many strategies, such as colorimetric (Chen et al, 2013), electrochemical (You, Bai, Yuan, Zhou, Bai, & Mu, 2018), fluorescence (Liu, Guan, Lv, Jiang, Yang, & Chen, 2014), and photoelectrochemical methods (Okoth, Yan, Liu, & Zhang, 2016). Among them, florescence method has received promising attention due to its fast response, simple operation and high sensitivity (Chen et al, 2018). However, the current fluorescence-based detection methods require laborious or expensive modification processes, which severely limit their practical applications (Cetin et al, 2014). SYBR Green I (SGI) is a popular commercial nucleic acid fluorescent dye that can specifically bind to double-stranded DNA (dsDNA) to produce strong fluorescent emission (Li, Tian, Kong, & Chu, 2015). Because SGI possesses temperature stability, good optical physical properties, and low fluorescent background in aqueous systems, florescence methods through SGI dyeing of dsDNA have been widely applied (Yang et al, 2018). Gold nanoparticles (AuNPs) have been used to construct many fluorescent or colorimetric sensors due to their dimensional and distance-dependent optical properties, high absorption efficiencies, and large surface areas (Niu, Lv, Liu, Bai, Yang, & Chen, 2014; Yang, Yin et al, 2017; Youssef, Abdel-Aziz, & El-Sayed, 2014). The dispersed AuNPs present red color, while a blue color can be observed when AuNPs aggregate in salt solutions (Mirkin, Letsinger, Mucic, & Storhoff, 1996). But ssDNA can prevent the salt-induced aggregation of AuNPs because of the protection of ssDNA by the coordination interaction between the exposed bases of ssDNA and the AuNPs (Li, & Rothberg, 2004). As a non-luminescent energy acceptor, AuNPs have a high extinction coefficient and a broad absorption spectrum in visible light, which may be utilized as quenchers by fluorescence methods based on the resonance energy transfer (FRET) or internal filter effect (IFE) (Wang, & Guo, 2009; Cao et al, 2013). 3
In the present study, a sensitive dichromatic aptasensor for SDM detection was constructed as shown in Fig.1. The affinity of aptamer toward AuNPs results in a complex of aptamer-AuNPs which can be deposited in residue in red color after centrifugation. In supernatant where the solo cDNA can’t be dyed by SGI so that no fluorescence emission is observed. In the presence of SDM, the specific binding of aptamer to SDM leads to the separation of AuNPs and aptamer-SDM after centrifugation, in which AuNPs is deposited in blue color in residue while the aptamer-SDM is dispersed in supernatant. After the addition of cDNA and SGI in supernatant, the hybridization of cDNA and aptamer occurs because aptamer shows higher affinity toward cDNA than SDM, which results in a fluorescence emission at 530 nm due to the dyeing of dsDNA by SGI. Based on the dichromatic aptasensor, SDM in fish and water was detected with the fluorescence in solutions and the color changes in residues.
2. Experimental
2.1 Reagents and materials DNA-aptamer against SDM (5´-GGC AAC GAG TGT TTA-3´) and its complementary strand DNA (cDNA, 5´-TAA ACA CTC GTT GCC-3´), and SYBR Green I (SGI) were synthesized by Sangon Biotechnology Co., Ltd. (Shanghai, China). Sulfadimethoxine (SDM) and sulfathiazole (ST) were purchased from Aladdin Reagent Co., Ltd. (Shanghai, China). Sulfaguanidine (SG), sulfanilamide (SN), chloramphenicol (CAP), chloroauric acid tetrahydrate (AuCl3·HCl·4H2O), and trisodium citrate dihydrate (C6H5Na3O7·2H2O) were purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). PAGE Pre-solution (Acr/Bis, 40%, 19:1) was purchased from Solarbio Science & Technology Co., Ltd (Beijing, China). TBE (5×) and DNA gel loading dye (6×) were 4
purchased from Beyotime Biotechnology Co., Ltd (Shanghai, China) and Thermo Fisher Scientific Co., Ltd (Shanghai, China), respectively. The GelRed nucleic acid dye was purchased from LIFE iLAB Biotechnology Co., Ltd (Shanghai, China). 10 mmol L-1 phosphate buffer (PBS) containing 1 mmol L-1 MgCl2 at pH 8.0 was used for both reactions of aptamer with cDNA and SDM. All chemicals were in analytical grade with no further purification. The water used in all the experiments was purified with H2O-I-2-TOC-T (18.2 MΩ cm, Germany). 2.2 Apparatus The pH values were measured with a FE 28 acidometer (Mettler Toledo International Trading Co., Ltd., Shanghai, China). Oil bath with heating and stirring was carried out by a MS-H-Pro+ LCD digital magnetic hotplate stirrer (Dragon Xingchuang Experiment Instrument Co., Ltd., Beijing, China). Vortex mixing was performed on a Vortex 3000 vortex mixer (Wiggens Labortechnik GmbH, Germany). The centrifugation was executed by a H1650-W centrifuge (Cence Laboratory Instrument Development Co., Ltd., Hunan, China). Fluorescence measurement was performed on a LS 55 Fluorescence Spectrometer (PerkinElmer Ltd., USA) at an excitation wavelength of 497 nm with excitation and emission slits both at 5 nm. The electrophoresis results were obtained using a DYY-6C electrophoresis apparatus (Liuyi Biotechnology Co., Ltd., Beijing, China) and a SynGene GeneGenius gel imaging system (Yitao Scientific Instrument Co., Ltd., Guangzhou, China). 2.3 Synthesis of AuNPs The preparation of AuNPs with an average diameter of 13 nm was referred from a previous report with some modification (Grabar, Freeman, Hommer, & Natan, 1995). Briefly, 1.03 mL of 20 mg mL-1 chlorauric acid and 49 mL of water were mixed in a cleaned flask and heated to 140 oC 5
with stirring. Subsequently, 5 mL of 38.8 mmol L-1 sodium citrate was added in boiling state with vigorous stirring until a burgundy color was observed. The mixture was kept boiling for 15 min, a colloidal solution was obtained and cooled to room temperature with continually stirring. The prepared AuNPs colloidal solution was stored in a 4 oC refrigerator for further use. The concentration of AuNPs was about 8.4 nmol L-1 calculated based on a molar extinction coefficient (ε) of 1.39×108 L·mol-1·cm-1 with the maximum absorbance at 520 nm (Haiss, Thanh, Aveyard, & Ferning, 2007; Chen, Lin, Hong, Zhong, Yao, & Huang, 2019). 2.4 The detection of SDM 50 μL aptamer was incubated with 50 μL of SDM solutions in different concentrations for 20 min in a multi-tube vortex mixer at room temperature. Then, 50 μL of AuNPs was added and incubated for another 10 min. After centrifuged at 13000 rpm for 7 min, 10 μL of SGI and 50 μL of cDNA were sequentially added into the supernatants, and stirred for 4 min. The fluorescence intensities of the supernatants were recorded at 530 nm at an excitation wavelength of 497 nm. Meanwhile, the color of residues was observed after mixing with 50 μL of PBS. 2.5 Gel electrophoresis A 12.5% nondenaturating polyacrylamide (PAGE) gel solution was prepared using 4% acrylamide in 1×TBE buffer (8.9 mmol L-1 Tris-Base, 8.9 mmol L-1 boric acid, 0.2 mmol L-1 EDTA, pH 8.3). After adding the gel in electrophoresis tanks, 10 μL of different samples containing DNA loading dyes (Marker, aptamer/SDM/cDNA, aptamer/cDNA, aptamer/SDM, and aptamer) were electrophoresed at 69 V for 60 min. Then, the gel was soaked in Gel Red dye for 15 min and photographed using a SynGene GeneGenius gel imaging system. 2.6 Detection of SDM in real samples 6
2.6.1 Water samples Water samples were collected from local fish farming pond and were filtered through 0.45 μm nylon membrane (Yang, Lin, Zhong, Chen, & Huang, 2017). The pH value was adjusted with 10 mmol L-1 of PBS solution. The test solution was prepared by mixing 1 mL of the water sample with detection regents as described above. 1 mL of different concentrations of SDM was spiked for recovery tests. 2.6.2 Fish samples Grass carp was purchased from a local supermarket and was pretreated based on literatures with some modification (Yang, Lin et al, 2017; Liu et al, 2017). Briefly, 5 g of grass carp muscle was homogenized (8000 rpm, 5 min) with 5 mL acetonitrile. After centrifugation, the supernatant was dried with N2. The residue was dissolved in 3 mL acetone, and was filtered through a 0.22 μm nylon membrane. The filtrate was purified with acetone twice. After dried, the residue was dissolved with 4 mL PBS solution, and further purified with 2 mL hexane. 1 mL of the PBS solution in substrate was used for SDM detection with the method described above. 1 mL SDM standard solution at different concentrations was spiked for recovery tests.
3. Results and discussion
3.1 Construction of the aptamersensor As shown in Fig.S1, the DNA aptamer against SDM consists of a loop and a stem with sequences of “GAG” and “GC-AT-AT”, by which SDM can be specifically recognized (Song et al, 2012). In the absence of target, the complexes of AuNPs-aptamer form by the coordination interaction between AuNPs and the bases of aptamer, and can be centrifuged and deposited in 7
residue with a red color. In the presence of SDM, aptamer specifically binds to SDM by forming a hairpin structure which encapsulates the aptamer bases, leading to the dissociation of aptamer from AuNPs. Therefore, the dissociative AuNPs aggregate in PBS solution and can be centrifuged in residue with a blue color. Most of the common design of aptasensors is based on the dissociation of aptamer-cDNA and the formation of aptamer-targets (You et al, 2018; Wang et al, 2019; Guo et al, 2018). On the contrary, in the present study, the aptamer-SDM is detached by cDNA, which requires that the affinity of the base complementary pairing rule between aptamer and cDNA should be much higher than that of the aptamer to SDM. In fact, the affinity between the aptamer and SDM is weak because of the relative large dissociation constant (Kd) of 84 nM which may be due to the few binding sites of the aptamers toward small target molecules (Song et al, 2012; Xu, Yuan, Chen, Xu, Wang, & Wu, 2012). The different affinities of the aptamer toward SDM and cDNA provide the possibility for the aptasensor design. Besides, the stem length of the aptamer is critical because the longer stem may be benefit for the higher affinity of the aptamer to SDM, but it will be difficult for the cDNA to detach the conjugates of aptamer-SDM to form dsDNA. In addition, the long stem of aptamer may cause high background fluorescence because the stem may be dyed by SGI after catching SDM as shown in Fig.2(b). The gel electrophoresis images in Fig.S2 show that the aptamers mixed with and without SDM respectively distributing in lane 3 and lane 4 present similar electrophoretic behaviors with no obvious fluorescent band. But the bright fluorescent bands can be observed in both lane 1 and lane 2, which indicates the presence of dsDNA in both atpamer/SDM/cDNA and apatmer/cDNA solutions. Both bands have the similar brightness and positions, revealing that the two solutions have the 8
similar dsDNA concentrations. The electrophoresis results demonstrate that the affinity of aptamer-cDNA is higher than that of aptamer-SDM in the detection conditions. After dyeing with SGI, the dsDNA generates a strong fluorescence at 530 nm as shown in Fig.2(e). In addition, the fluorescent intensity of aptamer/SDM/cDNA/SGI solution (Fig.2(d)) is nearly equal to that of aptamer/cDNA/SGI, indicating the detachment of the aptamer-SDM conjugates and the formation of dsDNA. In order to elevate the sensitivity of the aptasensor, AuNPs are removed by centrifugation based on the following reasons. Firstly, the fluorescence at 530 nm will be significantly quenched by AuNPs as shown in Fig.2(c). This may be due to the spectral overlap between the fluorescence peak and the absorption of AuNPs (as shown in Fig.S3), and the fluorescent quenching may be due to the inner filter effect (Yang, Mi, Cao, Zhang, Fan, & Hu, 2008; Xie, Huang, Zhang, Luo, & Li, 2012). Secondly, the excesses of aptamer can be removed from supernatants, by which the fluorescence from the excess aptamer dyed by SGI after adding cDNA (Fig.2(b)) can be eliminated. Based on the ingenious design, the aptasensor presents high sensitivity and stability for SDM detection. 3.2 Optimization of detection conditions The detection conditions including the concentration of aptamer, pH value of PBS, the concentration of MgCl2, and the molar ratio of aptamer to SGI were optimized as shown in Fig.S4. The optimized conditions were described as follows: 87.5 nmol L-1 of aptamer, pH 8.0 for PBS, 20 mmol L-1 MgCl2, and 1:15 molar ratio of aptamer to SGI. In addition, the concentration of cDNA was investigated. Result in Fig.S5 shows that the fluorescence intensities of the detection solutions increase with the concentration of cDNA until a plateau appearing at cDNA more than 109.4 nmol L-1. In order to completely detach the conjugates of aptamer-SDM, the concentration of cDNA was 9
109.4 nmol L-1. 3.2.1 Response time The response time of the aptasensor to SDM was tested. As shown in Fig.S6, the fluorescent emission is stable after 4 min. The result indicates that the detachment of the aptamer-SDM conjugates by cDNA and the dyeing of the dsDNA are rapid and sensitive. Therefore, the aptasensor can be used to detect SDM rapidly. 3.3 Linearity With the increases of SDM concentrations, the fluorescent intensities of the aptasensor increase as shown in Fig.3(a). Under the optimal conditions, two linear relationships between the values of F-F0 and SDM concentrations are established as shown in Fig.3(b), in which F and F0 are the fluorescent intensities of the aptasensor detected at 530 nm with a λex of 497 nm with and without SDM, respectively. The regression equation of F-F0=5.857C-0.379 (R2=0.998) is suitable for low SDM level (2-10 ng mL-1), and F-F0=0.866C+48.237 (R2=0.991) is suitable for high SDM level (10-300 ng mL-1).
3.4 Selectivity and interference Some veterinary drugs commonly used in aquaculture including sulfathiazole (ST), sulfaguanidine (SG), sulfanilamide (SN) and chloramphenicol (CAP) were selected to test the specificity of the aptasensor. Results in Fig.4 showed that no interference was observed for CAP, but slight interferences were found for SN, ST and SG which are the homologous of SDM with similar chemical structure of p-aminobenzenesulfonamide as shown in Fig.S7. Except for SN with 10
only p-aminobenzenesulfonamide, a bit more interference was observed for ST compared with SG, which may be due to the structure similarity of thiazole in ST. Pyrimidine and thiazole are the similar five-membered heterocyclic, while guanidine in SG is obviously different from SDM and ST. 3.5 Real sample measurement The aptasensor was applied to the detection of SDM in water and fish samples. The background concentration of water and fish samples is zero confirmed with HPLC as shown in Fig.S8. Data in Table 1 show that the recoveries for water samples ranged from 99.55% to 100.5% with relative standard deviations (RSDs) of 1.11% - 3.65%, and fish samples ranged from 99.2% to 102.0% with RSDs of 1.22%-2.11%. The results were validated by the method of HPLC as shown in Table 1, which demonstrates that the detection of SDM with the aptasensor is accurate and precise. The detection limits based on 3σ/K (n=9) are 3.41 ng mL-1 for aquaculture water and 4.41 ng g-1 for fish samples where σ is the standard deviation and K is the slope of linear equation for low SDM level. A comparison of the present work with previous reports is described as shown in Table 2, in which the as-prepared aptasensor offers an excellent detection limit. In order to test the stability and repeatability of the aptasensor, the intra and inter assays were carried out with water samples. Result in Table 3 shows that the highest RSDs for intra-assay and inter-assay are 5.8% and 8.2%, respectively, indicating that the aptasensor is stable and repeatable.
< Table 1> < Table 2> < Table 3> 11
4. Conclusions
A label-free aptasensor was constructed based on the different binding affinities of the aptamer toward to SDM and cDNA. By adding the AuNPs, the excessive aptamer which might hybride with cDNA was removed for eliminating the possible fluorescent interferences. And a dichromatic detection mode with the fluorescence at 530 nm and the color changes of AuNPs was achieved. Based on the subtle design of the aptasensor, SDM was detected with two linear ranges from 2 ng mL-1 to 300 ng mL-1 with detection limits of 3.41 ng mL-1 for aquaculture water and 4.41 ng g-1 for fish samples (3σ, n=9). The aptasensor has been successfully applied to the rapid detection of SDM in fish and water samples with high accuracy and sensitivity. But the aptasensor can only provide a rapid screening of SDM in samples, the results are better to be verified with instrumental methods, such as HPLC-tandem mass spectrometry. Acknowledgement This research was supported by the Foundation from the Science and Technology Planning Project of Fujian Province, China (2016Y0064), the Natural Science Foundation of Fujian Province of China (2018J01432, 2017J01633), National Key R and D Program of China (2018YFD0901003), the Science and Technology Planning Project of Xiamen, China (3502Z20183031), and the National Undergraduate Training Programs for Innovation and Entrepreneurship (201710390022, 201810390071, 20181xj008). References: Beltrán, M.C., Berruga, M.I., Molina, A., Althaus, R.L., & Molina, M.P. (2015). Performance of current microbial tests for screening antibiotics in sheep and goat milk. International dairy journal, 41, 13-15.
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Table and figure captions: Table 1. Recoveries of SDM in water and fish samples. Table 2. A comparison of different methods for the detection of SDM. Table 3. Intra-assay and inter-assay of SDM in water samples.
Fig.1 Schematic illustration for the detection principle of dichromatic label-free aptasensor. Fig.2 The fluorescence spectra of aptamer/SGI (a), aptamer/SDM/SGI (b), aptamer/AuNPs/cDNA/SGI (c), aptamer/SDM/cDNA/SGI (d), aptamer/cDNA/SGI (e). (aptamer, 87.5 nmol L-1; SDM, 300 ng mL-1; AuNPs, 2.1 nmol L-1; cDNA, 109.4 nmol L-1; SGI, 1.31 μmol L-1) Fig.3 Fluorescence spectra of solutions containing different concentrations of SDM (a); The relationship between the fluorescence recovery values (F-F0) and the concentrations of SDM (b). (F and F0 were the fluorescence intensities at 530 nm of the system in the presence and absence of SDM, respectively. Fig.4 Selectivity test of the aptasensor. Each of the concentrations was 0.32 μmol L-1. 15
16
Fig. 1 Schematic illustration for the detection principle of dichromatic label-free aptasensor.
100 2~10 ng mL-1: F-F0=5.857C-0.379; R2=0.998 10~300 ng mL-1: F-F0=0.866C+48.237; R2=0.991
0
0
50
100
150
200
250
300
Concentrations of SDM (ng mL-1) Fig.3 Fluorescence spectra of solutions containing different concentrations of SDM (a); The relationship between the fluorescence recovery values (F-F0) and the concentrations of SDM (b). (F and F0 were the fluorescence intensities at 530 nm of the system in the presence and absence of SDM, respectively.
200 0
160
ST
SG
SN
P CA
M ST +SG +SN CAP SD M+ + M DM M S SD SD SD
P
M +ST +SG +SN AP C + M M M SD SD SD SD M
F-F0
120 80 40 0 ST
SG
SN C A
SD
Fig.4 Selectivity test of the aptasensor. Each of the concentrations was 0.32 μmol L-1.
ST SG SN CAPSDM SDM+ST SDM+SG SDM+SN SDM+CAP 19
20
Table 1. Recoveries of SDM in water and fish samples. Samples
Spiked SDM (ng mL-1)
Fish culture water
Fish meat
Label-free aptasensor
HPLC
Measured values (ng mL-1)
Recoveries (%)
Measured values (ng mL-1)
Recoveries (%)
50
49.77±1.82
99.55±3.65
50.96±0.08
101.93±0.16
150
150.75±3.80
100.50±2.53
143.26±0.17
95.50±0.11
250
249.90±2.79
99.96±1.11
240.72±0.07
96.29±0.03
50
50.99±1.05
101.99±2.11
49.85±0.09
99.71±0.19
150
150.14±1.82
100.09±1.22
145.90±0.07
97.27±0.04
250
248.07±3.80
99.23±1.52
257.23±0.08
102.89±0.03
Table 2. A comparison of different methods for the detection of SDM. Methods
System
LOD
Colorimetric Electrochemical Electrochemical
Label-free aptasensor Photoelectrochemical sensor A molecular imprinted-based electrochemical sensor
50 ng mL-1 0.55 nmol L-1 21.7 μg mL-1
50-100 1.0-100 46.5-114
Fluorescence
A polymer-based aptasensor
10-100
Fluorescence
Label-free AuNPs-based aptasensor
10 ng mL-1 3.41 ng mL-1 for aquaculture water 4.41 ng g-1 for fish
