Determination of Saxitoxin by Aptamer-Based Surface-Enhanced Raman Scattering

Advances in Biosensors for the Rapid Detection of Marine Biotoxins: Current Status and Future Perspectives

Marine biotoxins (MBs), harmful metabolites of marine organisms, pose a significant threat to marine ecosystems and human health due to their diverse composition and widespread occurrence. Consequently, rapid and efficient detection technology is crucial for maintaining marine ecosystem and human health. In recent years, rapid detection technology has garnered considerable attention for its pivotal role in identifying MBs, with advancements in sensitivity, specificity, and accuracy. These technologies offer attributes such as speed, high throughput, and automation, thereby meeting detection requirements across various scenarios. This review provides an overview of the classification and risks associated with MBs. It briefly outlines the current research status of marine biotoxin biosensors and introduces the fundamental principles, advantages, and limitations of optical, electrochemical, and piezoelectric biosensors. Additionally, the review explores the current applications in the detection of MBs and presents forward-looking perspectives on their development, which aims to be a comprehensive resource for the design and implementation of tailored biosensors for effective MB detection.

Detection of saxitoxin by a SERS aptamer sensor based on enzyme cycle amplification technology

Saxitoxin (STX) is a typical toxic guanidinium neurotoxin, one of the paralytic shellfish poisons (PSP), which poses a serious threat to human health. In this paper, a simple and sensitive SERS aptamer sensor (abbreviated as AuNP@4-NTP@SiO₂) for the quantitative determination of STX was developed. Hairpin aptamers of saxitoxin are modified on magnetic beads and used as recognition elements. In the presence of STX, DNA ligase, and the rolling circle template (T1), a rolling circle amplification reaction was triggered to produce long single-stranded DNA containing repetitive sequences. The sequence can be hybridized with the SERS probe to realize the rapid detection of STX. Due to the inherent merits of its components, the obtained AuNP@4-NTP@SiO₂ SERS aptamer sensor manifests excellent sensing performance for STX detection with a wide linear range from 2.0 × 10^-10 mol L^-1 to 5.0 × 10^-4 mol L^-1 and a lower detection limit of 1.2 × 10^-11 mol L^-1. This SERS sensor can provide a strategy for the micro-detection of other biological toxins by changing the aptamer sequence.

SERS of cylindrospermopsin cyanotoxin: Prospects for quantitative analysis in solution and in fish tissue

Cylindrospermopsin (CYN), a cyanotoxin occurring in environmental waters as a cyanobacteria metabolite, has recently raised increased interest both in the scientific community and the environmental, food control and health care bodies due to the incidence of poisoning reports and the lack of prompt, effective detection and monitoring techniques. Here we report comprehensive Raman and SERS spectroscopy data on CYN cyanotoxin and provide a detailed characterization of the vibrational Raman signal based on DFT calculation as well as the adsorption properties with respect to the silver nanoparticles surface. Quantitative SERS analysis was achieved for concentrations range from 0.218 nM to 2.18 µM in aqueous solution. We further investigated the SERS discrimination of artificially intoxicated fish tissue from normal one, using linear discriminant analysis. Significant changes in SERS signal of toxic tissue compared to normal one allowed clear and fast differentiation of toxic tissue with 100% specificity/sensitivity. The cross-validation procedure provided 100% clear separation based on the SERS data. The results open reliable perspectives for SERS monitoring the environmental water bodies.

Recent advances in nanomaterials-based optical and electrochemical aptasensors for detection of cyanotoxins

The existence of cyanotoxins poses serious threats to human health, it is highly desirable to develop specific and sensitive methods for rapid detection of cyanotoxins in food and water. Due to the distinct advantages of aptamer including high specificity, good stability and easy preparation, various aptamer-based sensors (aptasensors) have been proposed to promote the detection of cyanotoxins. In this review, we summarize recent advance in optical and electrochemical aptasensors for cyanotoxins sensing by integrating with versatile nanomaterials or innovative sensing strategies, such as colorimetric aptasensors, fluorescent aptasensors, surface enhancement Raman spectroscopy-based aptasensors, voltammetric aptasensors, electrochemical impedance spectroscopy-based aptasensors and photoelectrochemical aptasensors. We highlight the accomplishments and advancements of aptasensors with improved performance. Furthermore, the current challenges and future prospects in cyanotoxins detection are discussed from our perspectives, which we hope to provide more ideas for future researchers.

Electrochemical biosensor with aptamer/porous platinum nanoparticle on round-type micro-gap electrode for saxitoxin detection in fresh water

Cyanotoxins are toxins produced by cyanobacteria; they negatively impact water resources used by humans and disrupt ecosystems worldwide. Among cyanotoxins, saxitoxin (STX) is a small molecule that causes paralysis in humans and contamination in freshwater resources. To monitor low concentration of STX levels, a sensitive and high fidelity detection system is required. In this study, a round-type micro-gap electrode (RMGE) was fabricated that provides the high signal fidelity for STX detection in real freshwater sample. The RMGE has the 15 pairs of identical electrode wire length between gap that gives the high signal fidelity. In addition, the sensitivity for STX detection was improved by introducing the porous platinum nanoparticle (pPtNP) that enahced the electrochemical sensitivity and the STX aptamer was used as the bioprobe. An electrochemical measurement method (square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS)) was introduced to construct STX biosensor. To evaluate the biosensor performance, the limit of detection (LOD) and selectivity test were performed on real freshwater samples. The biosensor demonstrated high selectivity even in freshwater samples over a wide linear concentration range of 10 pg/mL to 1 μg/mL and a detection limit of 4.669 pg/mL. These results suggest that the designed biosensor shows a wide range of possibilities for the detection of toxicants in freshwater that provide the new direction to the biosensor electrode design.

A Novel SELEX Based on Immobilizing Libraries Enables Screening of Saxitoxin Aptamers for BLI Aptasensor Applications

Saxitoxin (STX) is one of the potent marine biotoxins that has high rate of lethality. However, there are no effective treatments at present, and the existing detection methods need to be further explored because of ethical problems or technical limitations. In this work, oligonucleotide aptamers toward STX were screened based on immobilizing libraries on Immobilized Metal-Chelate (IMC), such as Ni-NTA Sepharose, and the IMC-SELEX was conducted by the G-quadruplex library and the random library, respectively. Aptamer 45e (from the G-quadruplex library) and aptamer 75a were obtained after optimization, and aptamer 45e turned out to have a higher affinity toward STX. Furthermore, it was found that the hydrogen bonding and the van der Waals forces (VDW) played major roles in the high efficiency and specificity between STX and 45e by means of molecular docking and dynamics simulation. Based on this, aptamer 45e-1 with the K_d value of 19 nM was obtained by further optimization, which was then used to construct a simple, label-free and real-time optical BLI aptasensor for the detection of STX. This aptasensor showed good reproducibility and stability. In summary, with the advantages of screening aptamers of high efficiency and specificity toward the targets, the proposed IMC-SELEX provides a promising screening strategy for discovering aptamers, which could be used as the potential molecular recognition elements in the fields of biomedicine, food safety and environmental monitoring.

Emerging roles of the aptasensors as superior bioaffinity sensors for monitoring shellfish toxins in marine food chain

Shellfish toxins are derived from harmful algae and are easily accumulated in environment and marine food through the food chain, exposing high risks on human health. Preliminary rapid screening is one of the most effective monitoring ways to reduce the potential risks; however, the traditional methods encounter with many limitations, such as complicated procedures, low sensitivity and specificity, and ethical problems. Alternatively, bioaffinity sensors are proposed and draw particular attention. Among them, the aptasensors are springing up and emerging as superior alternatives in recent years, exhibiting high practicability to analyze shellfish toxins in real samples in the marine food chain. Herein, the latest research progresses of aptasensors towards shellfish toxins in the marine food chain in the past five years was reviewed for the first time, in terms of the aptamers applied in these aptasensors, construction principles, signal transduction techniques, response types, individual performance properties, practical applications, and advantages/disadvantages of these aptasensors. Synchronously, critical discussions were given and future perspectives were prospected. We hope this review can serve as a powerful reference to promote further development and application of aptasensors to monitor shellfish toxins, as well as other analytes with similar demands.

A simple electrochemical aptasensor for saxitoxin detection

The combination between the electrochemical sensor and selective specificity of MB modified aptamer(MB-Apt) yielded an electrochemical aptasensor with a high sensitivity and excellent specific recognition ability to STX.

Recent advances in plasmonic Prussian blue-based SERS nanotags for biological application

The reliability and reproducibility of surface-enhanced Raman scattering (SERS) technology is still a great challenge in bio-related analysis. Prussian blue (PB)-based SERS tags have attracted increasing interest for improving these deficiencies due to its unique Raman band (near 2156 cm-1) in the Raman-silent region, providing zero-background bio-Raman labels without interference from endogenous biomolecules. Moreover, the stable PB shell consisting of multiple layers of CN- reporters ensure a stable and strong Raman signal output, avoiding the desorption of the Raman reporter from the plasmonic region by the competitive adsorption of the analyte. More importantly, they possess outstanding multiplexing potential in biological analysis owing to the adjustable Raman shift with unique narrow spectral widths. Despite more attention having been attracted to the structure and preparation of PB-based SERS tags for their better biological applications over the past five years, there is still a great challenge for SERS suitable for applications in the actual environment. The biological applications of PB-based SERS tags are comprehensively recounted in this minireview, mainly focusing on quantification analysis, multiple-spectral analysis and cell-imaging joint phototherapy. The prospects of PB-based SERS tags in clinical diagnosis and treatment are also discussed. This review aims to draw attention to the importance of SERS tags and provide a reference for the design and application of PB-based SERS tags in future bio-applications.

Electrochemical impedance biosensor for detection of saxitoxin in aqueous solution

Saxitoxin is a cyanotoxin which is very harmful to human health; the concentration limit in drinking water is only 3 μg/L. Therefore, a simple, fast, sensitive, low-cost, and specific method for its detection, quantification, and monitoring in water bodies is needed to avoid adverse effects on animal and human health. In this work, we developed an electrochemical impedimetric biosensor using a specific aptamer as recognition element for saxitoxin detection. This method allies the superior sensing characteristics of aptamers with the nondestructive, label-free, and easy working principles of the electrochemical impedance technique. The device presented sensitivity for detecting saxitoxin concentrations above 0.3 μg/L, with high selectivity in negative control experiments, demonstrating a promising alternative for water toxin detection.

An Electrochemical Ti3C2Tx Aptasensor for Sensitive and Label-Free Detection of Marine Biological Toxins

Saxitoxin (STX) belongs to the family of marine biological toxins, which are major contaminants in seafood. The reference methods for STX detection are mouse bioassay and chromatographic analysis, which are time-consuming, high costs, and requirement of sophisticated operation. Therefore, the development of alternative methods for STX analysis is urgent. Electrochemical analysis is a fast, low-cost, and sensitive method for biomolecules analysis. Thus, in this study, an electrolyte-insulator-semiconductor (EIS) sensor based on aptamer-modified two-dimensional layered Ti₃C₂T_x nanosheets was developed for STX detection. The high surface area and rich functional groups of MXene benefited the modification of aptamer, which had specific interactions with STX. Capacitance-voltage (C-V) and constant-capacitance (ConCap) measurement results indicated that the aptasensor was able to detect STX with high sensitivity and good specificity. The detection range was 1.0 nM to 200 nM and detection limit was as low as 0.03 nM. Moreover, the aptasensor was found to have a good selectivity and two-week stability. The mussel tissue extraction test suggested the potential application of this biosensor in detecting STX in real samples. This method provides a convenient approach for low-cost, rapid, and label-free detection of marine biological toxins.

A competitive colorimetric aptasensor transduced by hybridization chain reaction-facilitated catalysis of AuNPs nanozyme for highly sensitive detection of saxitoxin

Saxitoxin (STX) is a small molecule toxin (Mw. ca. 299 g/mol) with high acute toxicity, and it has urgent need of facile analytical methods. Herein, a competitive colorimetric aptasensor was developed for highly sensitive detection of STX. An anti-STX aptamer was hybridized with a complementary strand on the magnetic beads and was competitively bound by STX. The supernatant containing the aptamer binding to STX was obtained by magnetic separation, which could trigger hybridization chain reaction (HCR) to generate rigid double stranded DNAs (dsDNAs) with sticky end and variable length. These HCR-dsDNAs were found to be able to facilitate significant enhancement on the peroxidase-like catalytic capability of AuNPs nanozyme towards 3,3,5,5-tetramethylbenzidine (TMB). The concentration of STX was responded in a "turn on" mode, based on the amplified colorimetric transduction thereof. The aptasensor realized high sensitivity, with a limit of detection (LOD) as low as 42.46 pM. Moreover, a wide linear detection range of 78.13-2500 pM, good selectivity, as well as good recovery rates of 106.2-113.5% when analyzing STX in real shellfish samples were obtained. This strategy could be referred to develop robust aptasensors for simple and highly sensitive detection of other small molecules and toxins.

Recent Advances in Aptamer-Based Biosensors for Global Health Applications

Since aptamers were first reported in the early 2000s, research on their use for the detection of health-relevant analytical targets has exploded. This review article provides a brief overview of the most recent developments in the field of aptamer-based biosensors for global health applications. The review provides a description of general aptasensing principles and follows up with examples of recent reports of diagnostics-related applications. These applications include detection of proteins and small molecules, circulating cancer cells, whole-cell pathogens, extracellular vesicles, and tissue diagnostics. The review also discusses the main challenges that this growing technology faces in the quest of bringing these new devices from the laboratory to the market.

Recent progress in micro/nano biosensors for shellfish toxin detection

Shellfish toxins, as one kind of marine toxin, have attracted worldwide attention due to their severe threat to food safety and human health. Therefore, it is highly essential and urgent to develop a low-cost and convenient method to detect these toxins. With the rapid advance in microfabrication processes, micro/nano biosensors provide novel approaches to address this issue. In addition to their features of low cost, portability, easy operation, high efficiency and high bioactivity, micro/nano biosensors have great potential to realize on-the-spot, rapid detection of shellfish toxins. This review focuses on the most recent advances in the development of micro/nano biosensors for shellfish toxin detection. These biosensors are mainly classified into five categories according to their transducer detection principles, which include optical devices, electrochemical sensors, electrochemiluminescence, field-effect transistors, and acoustic devices. Sensor strategies, toxin analytes, biosensitive elements, coupling methods and field detection performance are highlighted to discuss the applications of shellfish toxin detection. With advances in sensor technology, biomaterials, microfabrication and miniaturized electronics, micro/nano biosensors applied to in-field fast detection of shellfish toxins are expected to play a critical role in food safety, environmental monitoring, and foreign trade in the foreseeable future. Finally, the current challenges and future development trends of micro/nano biosensors for shellfish toxin detection are discussed.

Ensuring seafood safe to spoon: a brief review of biosensors for marine biotoxin monitoring

With harmful algal blooms, marine food poisoning caused by marine biotoxins frequently occurs and is life-threatening if severe. However, the conventional detection methods of marine toxins have a few limitations: low sensitivity and high-cost. Therefore, it is necessary to establish a fast and sensitive on-site detection method for real seafood sample. Biosensors based on aptamers, antibodies, and cells have been applied in marine toxins monitoring. This review presents the classification and toxic effects of marine toxins, and recent biosensor for marine toxin detection. In addition, we have compared the superiority and limitation of these biosensors. Finally, challenges and opportunities of biosensors in food safety detection were discussed. Considering the excellent results achieved by the aptasensor in the field of detection, it seems ready to be put into practical applications.

Saxitoxin aptasensor based on attenuated internal reflection ellipsometry for seafood

In this study, we proposed label-free saxitoxin (STX) sensor using STX specific aptamer in combination with spectroscopic ellipsometry (SE) and attenuated internal reflection (AIR) spectroscopic ellipsometry method which is operated under surface plasmon resonance (SPR) conditions. Besides the other surface plasmon resonance-based applications, AIR-SE applications have unique advantages in terms of sensitivity and it was used herein for real-time detection of STX in real samples. Another method, SE, was also used and compared with AIR-SE. Analytical performances were satisfactory with low detection limits and a wide detection range. Limit of detection was 0.01 ng/mL for AIR-SE and 0.11 ng/mL for SE. Both proposed sensors were operable in 0.01 nM-1000 nM STX range. These methods were also used for the accurate, selective, and sensitive detection of STX from fish and shrimp samples.

Application of surface-enhanced Raman spectroscopy in fast detection of toxic and harmful substances in food

Surface-enhanced Raman spectroscopy (SERS) is being considered as a powerful technique in the area of food safety due to its rapidity, sensitivity, portability, and non-destructive features. This review aims to provide a comprehensive understanding of SERS applications in fast detection of toxic and harmful substances in food matrix. The enhancement mechanism of SERS, classification of active substrates, detection methods, and their advantages and disadvantages are briefly discussed in the review. The latest research progress of fast SERS detection of food-borne pathogens, mycotoxins, shellfish toxins, illegal food additives, and drug residues are highlighted in sections of the review. According to the current status of SERS detection of food-derived toxic and harmful substances, the review comes up with certain problems to be urgently resolved in SERS and brings up the perspectives on the future directions of SERS based biosensors.

Cys-functionalized AuNP substrates for improved sensing of the marine toxin STX by dynamic surface-enhanced Raman spectroscopy

Saxitoxin (STX) as one of the most harmful and typical paralytic shellfish toxins, is posing a serious threat to environmental and human health, thus it is essential to develop a sensitive and reliable analytical method for STX detection. Herein, we proposed a strategy for rapid and sensitive detection of STX with surface-enhanced Raman spectroscopy (SERS), by employing cysteine modified gold nanoparticles (Cys-AuNPs) as SERS probe to capture STX molecules through electrostatic interactions and multiple hydrogen bonds between Cys and STX molecules. Moreover, the XPS and zeta potential results indicated that Cys could bond to AuNPs through Au-S bonds and the addition of STX could induce the efficient aggregation of Cys-AuNPs owing to the presence of electrostatic interactions and multiple hydrogen bonds between Cys and STX molecules. Furthermore, considering the high sensitivity and stability of the dynamic surface-enhanced Raman spectroscopy (D-SERS) strategy with the formation of a 3D hotspot matrix, the highly sensitive detection of STX was realized to a level of 1 × 10^-7 M by using the D-SERS strategy. Consequently, Cys-AuNPs as high affinity substrates can provide high sensitivity for the detection of STX through the D-SERS strategy. Graphical abstract.

Aptamer-Based Biosensors for Environmental Monitoring

Due to their relative synthetic and chemical simplicity compared to antibodies, aptamers afford enhanced stability and functionality for the detection of environmental contaminants and for use in environmental monitoring. Furthermore, nucleic acid aptamers can be selected for toxic targets which may prove difficult for antibody development. Of particular relevance, aptamers have been selected and used to develop biosensors for environmental contaminants such as heavy metals, small-molecule agricultural toxins, and water-borne bacterial pathogens. This review will focus on recent aptamer-based developments for the detection of diverse environmental contaminants. Within this domain, aptamers have been combined with other technologies to develop biosensors with various signal outputs. The goal of much of this work is to develop cost-effective, user-friendly detection methods that can complement or replace traditional environmental monitoring strategies. This review will highlight recent examples in this area. Additionally, with innovative developments such as wearable devices, sentinel materials, and lab-on-a-chip designs, there exists significant potential for the development of multifunctional aptamer-based biosensors for environmental monitoring. Examples of these technologies will also be highlighted. Finally, a critical perspective on the field, and thoughts on future research directions will be offered.