A facile and sensitive SERS-based biosensor for colormetric detection of acetamiprid in green tea based on unmodified gold nanoparticles

Recent developments and applications of surface enhanced Raman scattering spectroscopy in safety detection of fruits and vegetables

This article reviewed the latest research progress of Surface-enhanced Raman Spectroscopy (SERS) in the security detection of fruits and vegetables in recent years, especially in three aspects: pesticide residues, microbial toxin contamination and harmful microorganism infection. The binding mechanism and application potential of SERS detection materials (including universal type and special type) and carrier materials (namely rigid and flexible materials) were discussed. Finally, the application prospect of SERS in fruit and vegetable safety detection was explored, and the problems to be solved and development trends were put forward. The poor stability and reproducibility of SERS substrates make it difficult for practical applications. It is necessary to continuously optimize SERS substrates and develop small and portable Raman spectroscopy analyzers. In the future, SERS technology is expected to play an important role in human health, food safety and economy.

A three-dimensional gold nanoparticles spherical liquid array for SERS sensitive detection of pesticide residues in apple

High-performance plasmonic substrates have recently attracted much research attention. Herein, a three-dimensional gold nanoparticles (AuNPs) spherical liquid array (SLA) with high "hot spots" and tunable nanometer gap by optimizing the proportion of AuNPs colloids over chloroform was synthesized based on a water-oil interfacial self-assembly strategy. The substrate demonstrated excellent surface-enhanced Raman scattering (SERS) performance using tetrathiafulvalene and rhodamine 6G (R6G) as probe molecules. With a simple extraction and soaking pretreatment process, the SLA exhibited high sensitivity for analysing triazophos on apple peels, with a limit of detection (LOD) of 0.005 µg/mL and recovery ranging from 96 to 110 %. Particularly, the chloroform produced an inherent characteristic peak at 665 cm-1, which was used as the internal standard to correct SERS signal fluctuation, leading to an improvement of the corresponding coefficient R2 from 0.97 to 0.99, thus improving the reproducibility. Therefore the SLA substrate possesses the potential for quantitative analysis of food contaminants.

Low-Cost Plant-Based Metal and Metal Oxide Nanoparticle Synthesis and Their Use in Optical and Electrochemical (Bio)Sensors

Technological progress has led to the development of analytical tools that promise a huge socio-economic impact on our daily lives and an improved quality of life for all. The use of plant extract synthesized nanoparticles in the development and fabrication of optical or electrochemical (bio)sensors presents major advantages. Besides their low-cost fabrication and scalability, these nanoparticles may have a dual role, serving as a transducer component and as a recognition element, the latter requiring their functionalization with specific components. Different approaches, such as surface modification techniques to facilitate precise biomolecule attachment, thereby augmenting recognition capabilities, or fine tuning functional groups on nanoparticle surfaces are preferred for ensuring stable biomolecule conjugation while preserving bioactivity. Size optimization, maximizing surface area, and tailored nanoparticle shapes increase the potential for robust interactions and enhance the transduction. This article specifically aims to illustrate the adaptability and effectiveness of these biosensing platforms in identifying precise biological targets along with their far-reaching implications across various domains, spanning healthcare diagnostics, environmental monitoring, and diverse bioanalytical fields. By exploring these applications, the article highlights the significance of prioritizing the use of natural resources for nanoparticle synthesis. This emphasis aligns with the worldwide goal of envisioning sustainable and customized biosensing solutions, emphasizing heightened sensitivity and selectivity.

Recent Advances in Aptasensors for Rapid Pesticide Residues Detection

Pesticides are applied widely to increase agricultural output and quality, however, this practice results in residual issues that not only harm the environment but also put people and animals' lives and health at risk. As a result, it is critical to find pesticide residues in a variety of sources, including crops, water supplies, and soil. Aptamers are more flexible in their synthesis and modification, have a high level of specificity, are inexpensive, and have good stability compared to conventional detection methods. They have therefore attracted a lot of interest in the industry. This study reviews the most recent aptasensor advancements in the detection of pesticide residues. Firstly, aptamers specifically binding to many pesticides are summarized. Secondly, the combination of aptasensors with colorimetric, fluorescent, surface enhanced Raman spectroscopy (SERS), resonance Light Scattering (RLS), chemiluminescence (CL), electrochemical, and electrochemiluminescence (ECL) technologies are systematically introduced, and their advantages and disadvantages are expounded. Importantly, the aptasensors for the detection of various pesticides (organochlorine, organophosphorus, neonicotinoids, carbamates, and pyrethroids) that have been developed so far are systematically analyzed and discussed. Finally, the furture prospects and challenges of the aptasensors are highlighted. It is expected to offer suggestions for the later creation of novel, highly effective and sensitive aptasensors for the detection of pesticide residues.

In silico selection of an aptamer for the design of aptamer-modified magnetic beads bearing ferrocene co-immobilized label for capacitive detection of acetamiprid

In silico evaluation of aptamer/target interactions can facilitate the development of efficient biosensor with high specificity and affinity. In this work, we present in silico, i.e. structural similarity, molecular docking and molecular dynamics selection of the aptamer with sufficient binding properties for acetamiprid (ACE), a nicotine-like pesticide, and its use to design aptamer-modified magnetic beads bearing ferrocene co-immobilized label for capacitive detection of ACE. Taking advantages of the aptamer higher stability and binding affinity, the specific properties of magnetic beads and the redox properties of ferrocene moiety, the developed aptasensor showed promising analytical performances for ACE detection, using electrochemical capacitance spectroscopy, with a linear response ranging from 1 fM to 100 pM and a limit of detection of 0.94 fM (S/N = 3). Furthermore, it was successfully applied to detect ACE in fortified tomatoes samples, proving a promising approach for routine detection of pesticide in real agricultural samples.

An aptamer-based colorimetric/SERS dual-mode sensing strategy for the detection of sulfadimethoxine residues in animal-derived foods

Residues of sulfadimethoxine (SDM) in animal-derived foods have attracted widespread public concern. Herein, we propose an aptamer-based colorimetric/SERS dual-mode sensing strategy for the determination of SDM based on hexadecyl trimethyl ammonium bromide (CTAB) induced aggregation of nanoparticles. In the absence of SDM, the SDM aptamer formed a supramolecular composite with CTAB, and the 4-mercaptopyrimidine functionalized gold nanoparticles (AuNPs@4-MPY) remained dispersed due to the lack of CTAB. Upon the addition of SDM, the SDM aptamer preferentially combined with SDM, resulting in the release of CTAB and subsequent aggregation of AuNPs@4-MPY, and the solution color changed from red to blue and presented a dynamic UV-absorbance curve based on different aggregation states. On the other hand, when, gold-silver core-shell nanoparticles (Au@AgNPs) were added additionally, the released CTAB narrowed the nanogap between AuNPs@4-MPY and Au@AgNPs, thus exhibiting enhanced SERS intensity of 4-MPY. This strategy achieved colorimetric detection of SDM with a linear range of 4.00-200.00 ng mL^-1 and a detection limit of 2.41 ng mL^-1, while SERS had a detection range of 1.20-120.00 ng mL^-1 with a detection limit of 0.89 ng mL^-1. This strategy is simple and cost-effective for the rapid detection of SDM within 20 minutes. It was further applied for the detection of SDM in spiked milk and honey samples with satisfactory recoveries. Therefore, it exhibits great potential for fast and on-site SDM detection.

A simple mesoporous silica Nanoparticle-based aptamers SERS sensor for the detection of acetamiprid

In this study, we developed a novel, rapid, simple, and sensitive nano sensor based on the controlled release of 4-Aminothiophenol (4-ATP) signal molecules from aptamers (Apts) modified aminated mesoporous silica nanoparticles (MSNs-NH₂) for the quantitative detection of acetamiprid (ACE). Firstly, we synthesized the positively charged MSNs-NH₂ by one-pot method, then loaded 4-ATP signal molecules into the pore, and finally electrostatically adsorbed the Apts onto the MSNs-NH₂, which acts as a gate to control the release of signal molecules. When ACE is added to the system, ACE preferentially and specifically binds to Apts, so the gate opens and 4-ATP signal molecules are released from the pore. Meanwhile, the silver-loaded mesoporous silica nanoparticles (Ag@SiO₂) were prepared by one-pot method as surface-enhanced Raman spectroscopy (SERS) substrate to amplify the signal. The intensity of 4-ATP signal molecules at 1433 cm^-1 position was observed to has a linear relationship with the concentration of ACE by SERS detection. Under the optimized detection conditions, a linear correlation was observed in the range of 5-60 ng/mL (R² = 0.99749), and the limit of detection (LOD) was 2.66 ng/mL. The method has high sensitivity, good selectivity and reproducibility, and can be used for actual sample analysis with the recovery rate of 96.24-103.6 %. This study provides a reference for the rapid and convenient detection of ACE in agricultural products.

A super-hydrophobic perfluoropolyether coated polytetrafluoroethylene sheets substrate for detection of acetamiprid surface-enhanced Raman spectroscopy

In this paper, a hydrophobic substrate as concentrators including an inner layer of polytetrafluoroethylene (PTFE) and an outer layer covered a thin layer of perfluoropolyether (PFPE) was constructed to achieve a higher sensitivity for acetamiprid (AC) SERS detection. The condensation effect of the PTFE-PFPE hydrophobic substrate-induced aggregation of gold nanoparticles (Au NPs) result ''hot spots'' for SERS. The hydrophobic substrate is better reproducibility (RSD < 5%) compared with that on a conventional silicon wafer. A further application of the hydrophobic substrate was demonstrated by the detection of AC in tea samples within a detection range of 0.03 mg/L to 3 mg/L. The hydrophobic substrate eliminates the problem of solution diffusion to avoid the "coffee ring" effect (When a droplet adheres to a solid surface, the suspended molecular particles usually deposit on the edge of the droplet to form a ring).

Progress on aptamer-based SERS sensors for food safety and quality assessment: methodology, current applications and future trends

It is well known that food safety has aroused extensive attentions from governments to researchers and to food industries. As a versatile technology based on molecular interactions, aptamer sensors which could specifically identify a wide range of food contaminants have been extensively studied in recent years. Surface-enhanced Raman spectroscopy integrated aptamer combines the advantages of both technologies, not only in the ability to specifically identify a wide range of food contaminants, but also in the ultra-high sensitivity, simplicity, portable and speed. To provide beneficial insights into the evaluation techniques in the field of food safety, we offer a comprehensive review on the design strategies for aptamer-SERS sensors in different scenarios, including non-nucleic acid amplification methods ("on/off" mode, sandwich mode, competition model and catalytic model) and nucleic acid amplification methods (hybridization chain reaction, rolling circle amplification, catalytic hairpin assembly). Meanwhile, a special attention is paid to the application of aptamer-SERS sensors in biological (foodborne pathogenic, bacteria and mycotoxins) and chemical contamination (drug residues, metal ions, and food additives) of food matrix. Finally, the challenges and prospects of developing reliable aptamer-SERS sensors for food safety were discussed, which are expected to offer a strong guidance for further development and extended applications.

Gold Nanoparticles Based Optical Biosensors for Cancer Biomarker Proteins: A Review of the Current Practices

Cancer prognosis depends on the early detection of the disease. Gold nanoparticles (AuNPs) have attracted much importance in biomedical research due to their distinctive optical properties. The AuNPs are easy to fabricate, biocompatible, surface controlled, stable, and have surface plasmonic properties. The AuNPs based optical biosensors can intensely improve the sensitivity, specificity, resolution, penetration depth, contrast, and speed of these devices. The key optical features of the AuNPs based biosensors include localized surface plasmon resonance (LSPR), SERS, and luminescence. AuNPs based biomarkers have the potential to sense the protein biomarkers at a low detection level. In this review, the fabrication techniques of the AuNPs have been reviewed. The optical biosensors based on LSPR, SERS, and luminescence are also evaluated. The application of these biosensors for cancer protein detection is discussed. Distinct examples of cancer research that have a substantial impact on both scientific and clinical research are presented.

Single molecule detection; from microscopy to sensors

Single molecule detection is necessary to find out physical, chemical properties and their mechanism involved in the normal functioning of body cells. In this way, they can provide a new direction to the healthcare system. Various techniques have been developed and employed for their successful detection. Herein, we have emphasized various traditional methods as well as biosensing technology which offer single molecule sensitivity. The various methods including plasmonic resonance, nanopores, whispering gallery mode, Simoa assay and recognition tunneling are discussed in the initial part which has been followed by a discussion about biosensor-based detection. Plasmonic, SERS, CRISPR/Cas, and other types of biosensors are focused in this review and found to be highly sensitive for single molecule detection. This review provides an overview of progression in different techniques employed for single molecule detection.

Surface Enhanced Raman Spectroscopy: Applications in Agriculture and Food Safety

Recent global warming has resulted in shifting of weather patterns and led to intensification of natural disasters and upsurges in pests and diseases. As a result, global food systems are under pressure and need adjustments to meet the change—often by pesticides. Unfortunately, such agrochemicals are harmful for humans and the environment, and consequently need to be monitored. Traditional detection methods currently used are time consuming in terms of sample preparation, are high cost, and devices are typically not portable. Recently, Surface Enhanced Raman Scattering (SERS) has emerged as an attractive candidate for rapid, high sensitivity and high selectivity detection of contaminants relevant to the food industry and environmental monitoring. In this review, the principles of SERS as well as recent SERS substrate fabrication methods are first discussed. Following this, their development and applications for agrifood safety is reviewed, with focus on detection of dye molecules, melamine in food products, and the detection of different classes of pesticides such as organophosphate and neonicotinoids.

Rapid detection and prediction of chloramphenicol in food employing label-free HAu/Ag NFs-SERS sensor coupled multivariate calibration

Considering growing food safety issues, hollow Au/Ag nano-flower (HAu/Ag NFs) nanosensor has been synthesized for label-free and ultrasensitive detection of chloramphenicol (CP) via integrating the surface-enhanced Raman scattering (SERS) and multivariate calibration. As the anisotropic plasmonic nanomaterials, HAu/Ag NFs had numerous nano-chink on their surface, which offered huge hotspots for analytes. CP generated a strong SERS signal while adsorbed on the surface of HAu/Ag NFs and noted excellent linearity with 1st derivative-competitive adaptive reweighted sampling-partial least squares (CARS-PLS) in the range of 0.0001-1000 µg/mL among the four applied multivariate calibrations. Additionally, CARS-PLS generated the lowest prediction error (RMSEP) of 0.089 and 0.123 µg/mL for milk and water samples, respectively, and any CARS-PLS model could be used for both samples according to T-test results (P > 0.05). The intra- and interday recovery for both samples were in the range of 92.62-96.74% with CV < 10%, suggested the proposed method has excellent accuracy and precision.

Advances in Surface-Enhanced Raman Scattering-Based Aptasensors for Food Safety Detection

Owing to the excellent performances of high sensitivity, high specificity, on-site detection, and multiplexing capability, surface-enhanced Raman scattering (SERS)-based aptasensors have performed prosperous applications and gained impressive progress in food safety. Herein, we reviewed the SERS-based aptasensors from the principles to specific applications in food safety. First, the sensor-working principles, SERS label design and preparation are introduced. Then, the popular platforms in the aptasensors are summarized with their advantages and disadvantages, followed by their representative applications. Further, the specific applications of developing SERS-based aptasensors in food safety are systematically provided. Moreover, the multiplex analysis using SERS labels are highlighted. Finally, challenges and perspectives for improving the SERS-based aptasensor performance are also discussed, aiming to give some proposes for researchers to choose suitable SERS-based aptasensors according to specific applications.

Facile Detection and Quantification of Acetamiprid Using a Portable Raman Spectrometer Combined with Self-Assembled Gold Nanoparticle Array

Rapid and facile determination of pesticides is critically important in food and environmental monitoring. This study developed a self-assembled gold nanoparticle array based SERS method for highly specific and sensitive detection of acetamiprid, a neonicotinoid pesticide that used to be difficult in SERS analysis due to its low affinity with SERS substrates. SERS detection and quantification of acetamiprid was conducted with self-assembled gold nanoparticle arrays at the interface of chloroform and water as the enhancing substrate. Since targets dissolved in chloroform (organic phase) also have access to the hot-spots of Au NP array, the developed method exhibited good sensitivity and specificity for acetamiprid determination. Under the optimal conditions, SERS intensities at Raman shifts of 631 cm−1 and 1109 cm−1 displayed a good linear relationship with the logarithm concentration of acetamiprid in the range of 5.0 × 10−7 to 1.0 × 10−4 mol/L (0.11335 ppm to 22.67 ppm), with correlation coefficients of 0.97972 and 0.97552, respectively. The calculated LOD and LOQ of this method were 1.19 × 10−7 mol/L (0.265 ppb) and 2.63 × 10−7 mol/L (0.586 ppb), respectively, using SERS signal at 631 cm−1, and 2.95 × 10−7 mol/L (0.657 ppb) and 3.86 × 10−7 mol/L (0.860 ppb) using SERS signal at 1109 cm−1, respectively. Furthermore, the developed SERS method was successfully applied in determining acetamiprid on the surface of apple and spinach. This method offers an exciting opportunity for rapid detection of acetamiprid and other organic pesticides considering its advantages of simple preparation process, good specificity and sensitivity, and short detection time (within 1 h).

In situ and rapid determination of acetamiprid residue on cabbage leaf using surface-enhanced Raman scattering

BACKGROUND

Pesticide residues in agricultural products and foods pose a serious threat to human health, and therefore a simple, rapid and direct method is urgently needed for pesticide residue detection. In addition to realizing the detection of acetamiprid in cabbage extract solution, the main target of this study was to establish an in situ surface-enhanced Raman scattering (SERS) method, which could directly detect acetamiprid residue on cabbage leaf without the need for extraction. Acetamiprid was first used to contaminate the surface of fresh cabbage leaf, and then bimetallic silver-coated gold nanoparticles (Au@AgNPs) were added on the contaminated spots and dried for SERS measurement.

RESULTS

Results suggested that acetamiprid can be detected in cabbage extract and on cabbage leaf surface in situ using the SERS method based on the Au@AgNPs substrate. The limit of detection was 0.08 μg mL^-1 in cabbage extract and 0.14 mg kg^-1 on cabbage leaf, the recovery ranged from 80.5% to 105.5% and the relative standard deviation was in the range 4.37-10.63%.

CONCLUSIONS

The proposed SERS method provides an in situ, nondestructive and rapid way to detect acetamiprid residue on the surface of fruits and vegetables, which could serve as an auxiliary approach for early screening of contaminated produce in field or on site in the future. © 2020 Society of Chemical Industry.

A multiple acetal chalcone-BODIPY-based fluorescence: synthesis, physical property, and biological studies

Fluorescent probes with outstanding physical and biological properties are superior for functional fluorescent dyes design. However, few studies pay attention to the stability of specific groups in fluorescent probes. The aldehyde group in the fluorescent probe is highly active but unstable under certain conditions. Therefore, we introduced ethoxy groups to realize the conversion to aldehyde groups under acidic conditions and avoid the instability of straightforward aldehyde groups. In this work, two fluorophores based on the multi acetal difluoroboraindacene (BODIPY) units with combination of the pharmaceutical intermediate chalcone have been firstly developed. In the design part, chalcone was introduced as a medium for fluorophore and multiple acetal. The mild synthesis strategy is based on the ligand ((Z)-2-chloro-1-(difluoroboranyl)-5-((4-ethyl-3,5-dimethyl-2H-pyrrol-2-ylidene)(phenyl)methyl)-1H-pyrrole) and connects with chalcone in (2E,2'E)-3,3'-(1,3-phenylene)bis(1-(2,4-bis(2,2-diethoxyethoxy)phenyl)prop-2-en-1-one). The emission wavelengths of the products are around 530 nm with high fluorescence intensity. To highlight the biological characteristics of these novel BODIPY fluorescents, we further demonstrated biological analysis studies on MTT and flow cytometry assays. The IC₅₀ values of BODIPY 5 ranged from 79 ± 6.11 to 63 ± 5.67 μM and BODIPY 6 were found to be 86 ± 4.07 to 58 ± 10.51 μM in tested cell lines. Flow cytometry data analysis shows that the representative agent 6 and reference have similar rational apoptosis rates in first quadrant. Last but not least, 6 shows outstanding biological compatibility and cell imaging potential in live cell imaging and in vivo assay, not only is the fluorescence prominent enough, but also rapidly distributes. Thus, our study reports a mild synthesis strategy and full biological analysis on BODIPY fluorescents, and the subtle modulation of the physical and biological properties by pharmaceutical substituents makes these designed chalcone-BODIPY-based dyes hopeful to realize drug functional fluorescent dyes. Two new highly sensitive BODIPY fluorophores are synthesized based on the ligand ((Z)-2-chloro-1-(difluoroboranyl)-5-((4-ethyl-3,5-dimethyl-2H-pyrrol-2-ylidene)(phenyl)methyl)-1H-pyrrole), which connects with chalcone in (2E,2'E)-3,3'-(1,3/4-phenylene)bis(1-(2,4-bis(2,2-diethoxyethoxy)phenyl)prop-2-en-1-one). Multiple acetals were introduced and the physical and biological properties of BODIPYs are described with MTT assay and in vitro and in vivo imaging.

Double-enzymes-mediated Fe2+/Fe3+ conversion as magnetic relaxation switch for pesticide residues sensing

It is a great challenge to develop a newly rapid and accurate detection method for pesticide residues. In this work, based on acetylcholinesterase (AChE) and choline oxidase (CHO), a double-enzymes-mediated Fe²⁺/Fe³⁺ conversion as magnetic relaxation switch was explored for the measurement of acetamiprid residue. In the double-enzymes reactions, acetylcholine chloride (ACh) can be catalyzed to produce choline by AChE, which is successively hydrolyzed to betaine and hydrogen peroxide (H₂O₂) by CHO. According to the enzyme inhibition principle, AChE activity will be inactivated in the presence of acetamiprid, thus leading to the less production of H₂O₂. Wherein, Fe²⁺, ACh, AChE and CHO were optimized as the reaction substrates. In the reaction system, acetamiprid can be reflected by the transverse relaxation time (T₂) that related with H₂O₂ mediated Fe²⁺ variations, which was further developed as an enzyme cascade amplification method. The detection linear range is 0.01∼1000 μg mL^-1 (R² = 0.99), and the limit of detection (LOD) is 2.66 ng mL^-1 (S/N = 3, n = 3), behaving a 335-fold improvement in LOD than that of traditional enzyme inhibition method (0.89 μg mL^-1). This method can realize "one-step mixing" detection of acetamiprid, which makes it a promising analytical tool for monitoring pesticide residue in complicated samples.

A Critical Factor for Quantifying Proteins in Unmodified Gold Nanoparticles-Based Aptasensing: The Effect of pH

Unmodified gold nanoparticles (AuNPs)-based aptasensing (uGA) assay has been widely implemented in the determination of many different targets, but there are few reports on protein detection using uGA. Here, we designed a uGA assay for protein detection including the elimination of interfering proteins. Positively charged protein can be absorbed directly on the surface of AuNPs to form “protein corona”, which results in the aggregation of AuNPs even without salt addition, thereby preventing target protein detection. To overcome this problem, we systematically investigated the effect of modifying the pH of the solution during the uGA assay. A probe solution with a pH slightly higher than the isoelectric points (pI) of the target protein was optimal for protein detection in the uGA assay, allowing the aptamer to selectively detect the target protein. Three proteins (beta-lactoglobulin, lactoferrin, and lysozyme) with different pI were chosen as model proteins to validate our method. Positively charged interfering proteins (with pIs higher than the optimal pH) were removed by centrifugation of protein corona/AuNPs aggregates before the implementation of actual sample detection. Most importantly, the limit of detection (LOD) for all three model proteins was comparable to that of other methods, indicating the significance of modulating the pH. Moreover, choosing a suitable pH for a particular target protein was validated as a universal method, which is significant for developing a novel, simple, cost-effective uGA assay for protein detection.

Selective determination of non-organophosphorus insecticide using DNA aptamer-based single-use biosensors

In the present study, we developed a disposable aptamer-based biosensor for rapid, sensitive, and reliable detection of acetamiprid (ACE). To improve the sensitivity of the aptasensor, poly-5-amino-2-mercapto-1,3,4-thiadiazole [P(AMT)] and gold nanoparticles (AuNPs) were progressively electrodeposited on the screen-printed electrode (SPE) surface by using cyclic voltammetry (CV) technique. For the determination of ACE, thiol-modified primary aptamer (Apt1) was selected by using the SELEX method and immobilized on the surface of the P(AMT) and AuNPs-modified SPE (SPE/P(AMT)/AuNPs) via AuS bonding. Then, the surface-bound aptamer was incubated with ACE for 45 Min. After that, the biotin-labeled aptamer 2 (Apt2) was interacted with the ACE, then the enzyme-labeled step was performed. In this step, alkaline phosphatase (ALP) was bound to the surface through the interaction between Apt2 labeled with biotin and streptavidin (strep)-ALP conjugate. The determination of ACE was achieved by measuring the oxidation signal of α-naphthol, which is formed on the electrode surface through the interaction of ALP with α-naphthyl phosphate. The working range of the developed aptasensor was determined as 5 × 10^-12 -5 × 10^-10  mol L^-1 with a low limit of detection (1.5 pmol L^-1 ). It was also found that the proposed aptasensor possessed great advantages such as low cost, good selectivity, and good reproducibility.

Impedimetric aptasensor based on highly porous gold for sensitive detection of acetamiprid in fruits and vegetables

A novel electrochemical aptasensor modified with highly porous gold and aptamer was prepared for the determination of acetamiprid in fruits and vegetables. Highly porous gold was synthesized by electroreduction at -4 V in an electrolyte containing 2.5 mol/L NH₄Cl and 10 mmol/L HAuCl₄. Acetamiprid-binding aptamer was immobilized on highly porous gold by self-assembly. Acetamiprid could be captured by aptamer on the sensing interface, resulting in an increment of electron transfer resistance. Thanks to the large specific surface area of highly porous gold and the high affinity of aptamer, the aptasensor exhibited a highly sensitive impedance response for acetamiprid. Under optimal condition, the aptasensor displayed a linear response for acetamiprid in the concentration range of 0.5-300 nmol/L, and the detection limit was 0.34 nmol/L. Furthermore, the aptasensor showed high selectivity, good reproducibility and stability. Finally, the aptasensor was applied for the determination of acetamiprid in fruits and vegetables with satisfactory results.

Dual amplification in a fluorometric acetamiprid assay by using an aptamer, G-quadruplex/hemin DNAzyme, and graphene quantum dots functionalized with D-penicillamine and histidine

D-penicillamine and histidine-functionalized graphene quantum dot (DPA-GQD-His) was synthesized and applied in a fluorometric method for determination of acetamiprid using a G-quadruplex DNAzyme. At first DNA probe (probe 1) consists of a target-specific aptamer with two arms of DNA segments. Probe 1 was hybridized with DNA probe 2 composed of a single DNA sequence with two split G-rich DNA sequences. This leads to the formation of a triplex-to-G-quadruplex (TPGQ). Next, acetamiprid was hybridized with the aptamer in the TPGQ to release free DNA probe 2. The released probe 2, in the presence of of K⁺, undergoes a structural change into a stem-loop structure (by self-complementary hybridization and Hoogsteen hydrogen bonding) that bears a G-quadruplex structure. This is followed by conjugation with hemin to form the G-quadruplex/hemin DNAzyme. The DNAzyme catalyzes the oxidation of o-phenylenediamine by H₂O₂ to produce a yellow fluorescent product with excitation/emission maxima at 420/560 nm. The oxidation product interacts with DPA-GQD-His to achieve a rapid energy transfer between DPA-GQD-His and oxidation product. This increases the fluorescence of the oxidation product and quenches the fluorescence of DPA-GQD-His. DPA-GQD-His also improves the catalytic activity of DNAzyme towards oxidation of ophenylenediamine oxidization and enhances fluorometric response to acetamiprid. The assay works in the 1.0 fM to 1.0 nM acetamiprid concentration range and has a 0.38 fM detection limit. It was successfully applied to the determination of acetamiprid in tea. Graphical abstractThe study reported one double amplification strategy for ultrasensitive fluorescence detection of acetamiprid in tea with D-penicillamine and histidine-functionalized graphene quantum dots and G-quadruplex/heminDNAzyme. The analtyical method exhibits ultra high sensitivity, selectivity and rapidity of fluorescence response to acetamiprid.

Rapid quantitative analysis of Hg2+ residue in dairy products using SERS coupled with ACO-BP-AdaBoost algorithm

In this study, surface-enhanced Raman spectroscopy (SERS) coupled with multivariate calibrations were employed to develop a rapid, simple and sensitive method for determination of mercury ions residues in dairy products. Initially, spherical Au@SiO₂ core shell nanoparticles with highly enhancement effect were synthesized to serve as the SERS substrate. Afterwards, an optical sensor system, namely micro-Raman spectroscopy system, was constructed for rapid acquisition of Au@SiO₂-mercury ions spectra. Then, ant colony optimization (ACO) and genetic algorithm (GA) were applied comparatively for selecting the characteristic variables from the Savitzky Golay-First derivative (SG-FD) processing data for subsequent quantitative analysis. Eventually, both linear (PLS and SW-MLR) and nonlinear (BPANN and BP-AdaBoost) methods were used for modeling. Experimental results showed that the variables selection methods significantly improved the model performance. Especially for the ACO algorithm, and the ACO-BP-AdaBoost model achieved the best results with the higher correlation coefficient of determination (R² = 0.997), and lower root-mean-square error of prediction (RMSEP = 0.092) than other quantification models. Paired sample t-test exhibited no statistically significant difference (sig > 0.05) between the reference concentrations determined by inductively coupled plasma mass spectrometry (ICP-MS) and the predicted concentrations by ACO-BP-AdaBoost model in adulterated foodstuffs.

Development and Application of Aptamer-Based Surface-Enhanced Raman Spectroscopy Sensors in Quantitative Analysis and Biotherapy

Surface-enhanced Raman scattering (SERS) is one of the most special and important Raman techniques. An apparent Raman signal can be observed when the target molecules are absorbed onto the surface of the SERS substrates, especially on the "hot spots" of the substrates. Early research focused on exploring the highly active SERS substrates and their detection applications in label-free SERS technology. However, it is a great challenge to use these label-free SERS sensors for detecting hydrophobic or non-polar molecules, especially in complex systems or at low concentrations. Therefore, antibodies, aptamers, and antimicrobial peptides have been used to effectively improve the target selectivity and meet the analysis requirements. Among these selective elements, aptamers are easy to use for synthesis and modifications, and their stability, affinity and specificity are extremely good; they have been successfully used in a variety of testing areas. The combination of SERS detection technology and aptamer recognition ability not only improved the selection accuracy of target molecules, but also improved the sensitivity of the analysis. Variations of aptamer-based SERS sensors have been developed and have achieved satisfactory results in the analysis of small molecules, pathogenic microorganism, mycotoxins, tumor marker and other functional molecules, as well as in successful photothermal therapy of tumors. Herein, we present the latest advances of the aptamer-based SERS sensors, as well as the assembling sensing platforms and the strategies for signal amplification. Furthermore, the existing problems and potential trends of the aptamer-based SERS sensors are discussed.