A coordination polymer nanobelt (CPNB)-based aptasensor for sulfadimethoxine

An aptamer sensor based on AgNPs@MOF for surface-enhanced Raman spectroscopy detection of sulfadimethoxine in food

A highly sensitive aptamer sensor (aptasensor) is proposed based on metal-organic frameworks-silver nanoparticles (AgNPs@MOF) to detect sulfadimethoxine (SDM) by surface-enhanced Raman spectroscopy (SERS). AgNPs@MOF with SERS activity was successfully fabricated by synthesizing AgNPs in situ on the surface of MIL-101(Fe), and SDM aptamer and Raman reporter 4-aminophenthiophenol (4-ATP) were selected as specific recognition elements and signal probes, respectively. When SDM was absent, the SDM aptamers were effectively adsorbed on the surface of AgNPs@MOF, thus keeping AgNPs@MOF in a dispersed state, resulting in a weakened SERS signal of 4-ATP. In the presence of SDM, the combination of SDM and aptamer formed a rigid hairpin SDM-aptamer complex, which bound less to AgNPs@MOF. Therefore, fewer aptamers were adsorbed on AgNPs@MOF, which exposed more hot spots, resulting in an enhanced SERS signal of 4-ATP. The aptasensor had good selectivity and sensitivity towards SDM and a good linear relationship between SERS intensity and SDM concentration in the range 6.00-150.00 ng/mL, with the limit of detection as low as 2.73 ng/mL. Further application to honey and chicken samples spiked with SDM resulted in satisfactory recoveries, and the aptasensor showed good stability and reproducibility in real samples. The aptasensor based on AgNPs@MOF was proposed for the first time to detect trace SDM by SERS, which provided a favorable way to develop various sensing platforms for antibiotic detection in food safety.

An inverted tetrahedron-mediated DNA walker for sulfadimethoxine detection

An inverted DNA tetrahedron-mediated modular DNA walker was developed for the determination of sulfadimethoxine. The inverted DNA tetrahedron scaffold raises several advantages of recognition module including appropriate lateral space, multiple recognition domains, and cost-effectiveness. The proposed inverted DNA tetrahedron-based recognition module exhibited better binding affinity and kinetics toward target antibiotic than that of other DNA tetrahedron counterparts. Upon specific binding with target, the released bipedal DNA walking strand hops to the signal amplification module and moves stochastically with assistant of nicking enzyme. By coupling these two modules, a good linear relationship between the fluorescence intensity of supernatant and the concentration of sulfadimethoxine was achieved in the range 0.1-100 nM, and the limit of detection was 64.7 pM. Furthermore, this modular DNA walker had also successfully applied to spiked honey and milk samples with satisfactory recoveries from 91.5 to 108.8%, demonstrating its practical sensing capability.

Electrochemical biosensor for rapid and sensitive monitoring of sulfadimethoxine based on nanoporous carbon and aptamer system

In this study, a straightforward electrochemical aptasensor was developed to detect sulfadimethoxine (SDM). It included a glassy carbon electrode decorated by boron nitride quantum dots (BNQDs) and aptamer-functionalized nanoporous carbon (APT/CZ). CZ was first synthesized by calcinating a zeolitic imidazolate framework (ZIF-8). Then, the electroactive dye methylene blue (MB) was entrapped inside its pores. By attaching aptamer to the CZ surface, APT/CZ acted as a bioguard, which prevented the MB release. Therefore, the electrochemical signal of the entrapped MB was high in the absence of SDM. Introducing SDM caused the conformation of aptamers to change, and a large number of MB was released, which was removed by washing. Therefore, the detection strategy was done based on the change in the electrochemical signal intensity of MB. The aptasensor was applied to detect SDM at a concentration range of 10-17 to 10-7 M with a detection limit of 3.6 × 10-18 M.

Aptamer-Based fluorescent DNA biosensor in antibiotics detection

The inappropriate employment of antibiotics across diverse industries has engendered profound apprehensions concerning their cumulative presence within human bodies and food commodities. Consequently, many nations have instituted stringent measures limiting the admissible quantities of antibiotics in food items. Nonetheless, conventional techniques employed for antibiotic detection prove protracted and laborious, prompting a dire necessity for facile, expeditious, and uncomplicated detection methodologies. In this regard, aptamer-based fluorescent DNA biosensors (AFBs) have emerged as a sanguine panacea to surmount the limitations of traditional detection modalities. These ingenious biosensors harness the binding prowess of aptamers, singular strands of DNA/RNA, to selectively adhere to specific target antibiotics. Notably, the AFBs demonstrate unparalleled selectivity, affinity, and sensitivity in detecting antibiotics. This comprehensive review meticulously expounds upon the strides achieved in AFBs for antibiotic detection, particularly emphasizing the labeling modality and the innovative free-label approach. It also elucidates the design principles behind a diverse array of AFBs. Additionally, a succinct survey of signal amplification strategies deployed within these biosensors is provided. The central objective of this review is to apprise researchers from diverse disciplines of the contemporary trends in AFBs for antibiotic detection. By doing so, it aspires to instigate a concerted endeavor toward the development of heightened sensitivity and pioneering AFBs, thereby contributing to the perpetual advancement of antibiotic detection methodologies.

Multiplexed SELEX for Sulfonamide Antibiotics Yielding a Group-Specific DNA Aptamer for Biosensors

The widespread use of sulfonamide (SA) antibiotics in animal husbandry has led to residues of SAs in the environment, causing adverse effects to the ecosystem and a risk of bacterial resistance, which is a potential threat to public health. Therefore, it is highly desirable to develop simple, high-throughput methods that can detect multiple SAs simultaneously. In this study, we isolated aptamers with different specificities based on a multi-SA systematic evolution of ligands by the exponential enrichment (SELEX) strategy using a mixture of sulfadimethoxine (SDM), sulfaquinoxaline (SQX), and sulfamethoxazole (SMZ). Three aptamers were obtained, and one of them showed a similar binding to all tested SAs, with dissociation constant (Kd) ranging from 0.22 to 0.63 μM. For the other two aptamers, one is specific for SQX, and the other is specific for SDM and sulfaclozine. A label-free detection method based on the broad-specificity aptamer was developed for the simultaneous detection of six SAs, with detection of limits ranging from 0.14 to 0.71 μM in a lake water sample. The aptasensor has no binding for other broad-spectrum antibiotics such as β-lactam antibiotics, quinolones, tetracyclines, and chloramphenicol. This work provides a promising biosensor for rapid, multiresidue, and high-throughput detection of SAs, as well as a shortcut for the preparation of different specific recognition elements required for the detection of broad-spectrum antibiotics.

An upconversion biosensor based on inner filter effect for dual-role recognition of sulfadimethoxine in aquatic samples

Sulfadimethoxine (SDM) as an extensively employed veterinary drug causes potential threats to human health. Herein, a dual recognition mode novel upconversion fluorescence biosensor was designed based on inner filter effect (IFE) to sensitively and rapidly detect SDM in aquatic samples. Aldehyde-functionalized magnetic nanoparticles (MNPs) were applied to recognize and capture SDM, followed by specifically bond with biotin-labeled aptamers. The upconversion nanoparticles and the colored products resulting from the enzyme-catalyzed oxidation of 3,3,5,5-tetramethylbenzidine exhibited an IFE quenching process. Under the optimal condition, the results displayed the fluorescence intensity was correlated with the concentration of SDM within the range of 0.5-1000 ng⋅mL-1 achieving a low limit of detection of 0.13 ng⋅mL-1. The SDM detection system was further employed in the spiked aquatic samples with good recoveries (88.41-96.78 %). Consequently, the constructed fluorescence biosensor provided broad prospects for accuracy and rapid detection of SDM.

New two-dimensional nanocomposites combined with target-induced strategy in an electrochemical aptasensor for sensitive determination of sulfadimethoxine

Ni-Zn bimetallic organic framework nanosheets (NiZn-MOF NSs) were modified onto PEI-functionalized MXene for the first time. The combination of the two kinds of nanosheets forms a sensing platform with superior conductivity and biocompatibility. On this basis, a highly sensitive biosensor was developed for the determination of sulfadimethoxine (SDM). Furthermore, Au and Mn nanoparticles decorated reduced graphene oxide (Au-Mn/rGO) was introduced as a signal hindering molecule under the target-induced amplification strategy. When the Au-Mn/rGO-labelled SDM-binding aptamer (Au-Mn/rGO-SBA) specifically bound to target SDM, it detached from the electrode, thereby further amplifying the electrochemical signal of [Fe(CN)6]3-/4-. The developed aptasensor for SDM showed excellent response signals in the range 1 pg mL-1 to 100 ng mL-1, with a limit of detection (LOD) as low as 0.22 pg mL-1. Significantly, the proposed sensor also showed satisfactory results in milk samples with recoveries ranging from 87.0 to 96.4% and RSD from 1.5 to 5.1%, which is believed to be useful in food safety assays.

A signal "on-off-on"-type electrochemiluminescence aptamer sensor for detection of sulfadimethoxine based on Ru@Zn-oxalate MOF composites

An "on-off-on"-type electrochemiluminescence (ECL) aptamer sensor based on Ru@Zn-oxalate metal-organic framework (MOF) composites is constructed for sensitive detection of sulfadimethoxine (SDM). The prepared Ru@Zn-oxalate MOF composites with the three-dimensional structure provide good ECL performance for the "signal-on." The MOF structure with a large surface area enables the material to fix more Ru(bpy)₃²⁺. Moreover, the Zn-oxalate MOF with three-dimensional chromophore connectivity provides a medium which can accelerate excited-state energy transfer migration among Ru(bpy)₃²⁺ units, and greatly reduces the influence of solvent on chromophore, achieving a high-energy Ru emission efficiency. The aptamer chain modified with ferrocene at the end can hybridize with the capture chain DNA1 fixed on the surface of the modified electrode through base complementary pairing, which can significantly quench the ECL signal of Ru@Zn-oxalate MOF. SDM specifically binds to its aptamer to separate ferrocene from the electrode surface, resulting in a "signal-on" ECL signal. The use of the aptamer chain further improves the selectivity of the sensor. Thus, high-sensitivity detection of SDM specificity is realized through the specific affinity between SDM and its aptamer. This proposed ECL aptamer sensor has good analytical performance for SDM with low detection limit (27.3 fM) and wide detection range (100 fM-500 nM). The sensor also shows excellent stability, selectivity, and reproducibility, which proved its analytical performance. The relative standard deviation (RSD) of SDM detected by the sensor is between 2.39 and 5.32%, and the recovery is in the range 97.23 to 107.5%. The sensor shows satisfactory results in the analysis of actual seawater samples, which is expected to play a role in the exploration of marine environmental pollution.

Different Strategies for the Microfluidic Purification of Antibiotics from Food: A Comparative Study

The presence of residual antibiotics in food is increasingly emerging as a worrying risk for human health both for the possible direct toxicity and for the development of antibiotic-resistant bacteria. In the context of food safety, new methods based on microfluidics could offer better performance, providing improved rapidity, portability and sustainability, being more cost effective and easy to use. Here, a microfluidic method based on the use of magnetic microbeads specifically functionalized and inserted in polymeric microchambers is proposed. The microbeads are functionalized either with aptamers, antibodies or small functional groups able to interact with specific antibiotics. The setup of these different strategies as well as the performance of the different functionalizations are carefully evaluated and compared. The most promising results are obtained employing the functionalization with aptamers, which are able not only to capture and release almost all tetracycline present in the initial sample but also to deliver an enriched and simplified solution of antibiotic. These solutions of purified antibiotics are particularly suitable for further analyses, for example, with innovative methods, such as label-free detection. On the contrary, the on-chip process based on antibodies could capture only partially the antibiotics, as well as the protocol based on beads functionalized with small groups specific for sulfonamides. Therefore, the on-chip purification with aptamers combined with new portable detection systems opens new possibilities for the development of sensors in the field of food safety.

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.

Dual fluorescent aptasensor for simultanous and quantitative detection of sulfadimethoxine and oxytetracycin residues in animal-derived foods tissues based on mesoporous silica

Herein, we developed a dual fluorescent aptasensor based on mesoporous silica to simultaneously detect sulfadimethoxine (SDM) and oxytetracycline (OTC) in animal-derived foods. We immobilized two types of aptamers modified with FAM and CY5 on the silica surface by base complementary pairing reaction with the cDNA modified with a carboxyl group and finally formed the aptasensor detection platform. Under optimal conditions, the detection range of the aptasensor for SDM and OTC was 3-150 ng/mL (R ² = 0.9831) and 5-220 ng/mL (R ² = 0.9884), respectively. The limits of detection for SDM and OTC were 2.2 and 1.23 ng/mL, respectively. The limits of quantification for SDM and OTC were 7.3 and 4.1 ng/mL, respectively. Additionally, the aptasensor was used to analyze spiked samples. The average recovery rates ranged from 91.75 to 114.65% for SDM and 89.66 to 108.94% for OTC, and all coefficients of variation were below 15%. Finally, the performance and practicability of our aptasensor were confirmed by HPLC, demonstrating good consistency. In summary, this study was the first to use the mesoporous silica-mediated fluorescence aptasensor for simultaneous detection of SDM and OTC, offering a new possibility to analyze other antibiotics, biotoxins, and biomolecules.

Broad-Specificity Aptamer of Sulfonamides: Isolation and Its Application in Simultaneous Detection of Multiple Sulfonamides in Fish Sample

Sulfonamide antibiotics (SAs) are widely used in animal husbandry and aquaculture, and the excess residues of SAs in animal-derived foods will harm the health of consumers. In reality, various SAs were alternately used in animal husbandry and aquaculture, and thus, it is urgent need to develop simple and high-throughput methods for simultaneously detecting multiple SAs or groups of SAs in order to realize rapid screening of total SAs residues in animal-derived foods. We herein isolated a broad-specificity aptamer for SAs by using a multi-SAs systematic evolution of ligands by exponential enrichment (SELEX) strategy. The isolated broad-specificity aptamer has a higher binding affinity to five different SAs including sulfaquinoxaline (SQ), sulfamethoxypyridazine (SMPZ), sulfametoxydiazine (SMD), sulfachloropyridazine (SCP), and sulfapyridine (SPD) and, thus, can be used as a bioreceptor for developing various high-throughput methods for the simultaneous detection or rapid screening of above five SAs. Based on the isolated broad-specificity aptamer and Cy7 (diethylthiatricarbocyanine) displacement strategy, a colorimetric aptasensor was developed for the simultaneous detection of SQ, SMPZ, SMD, SCP, and SPD with a visual detection limit of 2.0-5.0 μM and a spectrometry detection limit of 0.2-0.5 μM. The colorimetric aptasensor was successfully used to detect SQ, SMPZ, SMD, SCP, and SPD in fish muscle with a recovery of 82%-92% and a RSD (n = 5) < 7%. The success of this study provided a promising bioreceptor for developing various high-throughput methods for on-site rapid screening of multiple SAs residues, as well as a simple method for the rapid and cost-effective screening of total SQ, SMPZ, SMD, SCP, and SPD in seafood.

High-Sensitive FAM Labeled Aptasensor Based on Fe3O4/Au/g-C3N4 for the Detection of Sulfamethazine in Food Matrix

In this study, we developed a fluorescent aptasensor based on Fe₃O₄/Au/g-C₃N₄ and a FAM-labeled aptamer (FAM-SMZ1S) against sulfamethazine (SMZ) for the specific and sensitive detection of SMZ in food matrix. The FAM-SMZ1S was adsorbed by the Fe₃O₄/Au/g-C₃N₄ via π–π stacking and electrostatic adsorption, serving as a basis for the ultrasensitive detection of SMZ. Molecular dynamics was used to explain the reasons why SMZ1S and SMZ were combined. This aptasensor presented sensitive recognition performance, with a limit of detection of 0.16 ng/mL and a linear range of 1–100 ng/mL. The recovery rate ranged from 91.6% to 106.8%, and the coefficient of variation (CV) ranged from 2.8% to 13.4%. In addition, we tested the aptasensor for the monitoring of SMZ in various matrix samples, and the results were well-correlated (R² ≥ 0.9153) with those obtained for HPLC detection. According to these results, the aptasensor was sensitive and accurate, representing a potentially useful tool for the detection of SMZ in food matrix.

DNA-Crosslinked 2D Photonic Crystal Hydrogels for Detection of Adenosine Actuated by an Adenosine-Binding Aptamer

There is a need to develop versatile sensing motifs that can be used to detect a variety of chemical targets in resource-limited settings, for example, at the point of care. While numerous sensing technologies have been developed toward this effort, these technologies can be overly complex and require a skilled technician, extensive sample preparation, or sophisticated instrumentation to use, limiting their generalizability and application in resource-limited settings. Here, we report a novel sensing motif that utilizes DNA-crosslinked two-dimensional photonic crystal (2DPC) hydrogels. These hydrogel sensors contain a DNA aptamer recognition group that binds a target analyte. As proof of concept, we fabricated 2DPC hydrogels using a well-studied adenosine-binding aptamer. This adenosine aptamer is duplexed with a partially complementary strand and forms responsive crosslinks in the hydrogel polymer network. When adenosine is introduced, aptamer-adenosine binding occurs, breaking the DNA crosslinks and causing the hydrogel to swell. This in turn increases the particle spacing of an embedded 2DPC array, shifting the 2DPC Bragg diffraction. Thus, adenosine concentration can be monitored through 2DPC Bragg diffraction measurements. A linear range of 20 μM to 2 mM was observed. The detection limits were calculated to be 13.9 μM in adenosine-binding buffer and 26.7 μM in fetal bovine serum. This reported sensing motif has a readout that is simple and rapid and requires minimal equipment. We hypothesize that this sensing motif is generalizable and that other sensors can be easily fabricated by simply exchanging the aptamer that serves as a molecular recognition group.

Aptamer-conjugated MoS2 for enrichment and direct detection of small molecules in laser desorption/ionization mass spectrometry

In this work, MoS₂ nanosheets were synthesized by the chemical exfoliation method and then modified with a thiol-terminated aptamer via a simple thiol functionalization route. The as-made nanomaterial was characterized by UV-vis absorption spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and transmission electron microscopy. By integrating the advantages of MoS₂ nanosheets and the recognition ability of aptamers, the functionalized nanomaterial has been successfully employed for simultaneous enrichment and analysis of sulfadimethoxine by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS). The aptamer-conjugated MoS₂ showed an excellent capture ability to eliminate background signals from the species co-existing in a milk sample. The simplicity of the synthesis method and the excellent performance of aptamer-conjugated MoS₂ make it an ideal candidate for application in selective MS analysis of the target analyte from complex samples.

Microfluidic flow-injection aptamer-based chemiluminescence platform for sulfadimethoxine detection

Gold nanoparticle–catalyzed chemiluminescence (CL) of luminol is an attractive alternative to strategies relying on enzymes, as their aggregation leads to significantly enhanced CL signals. Consequently, analytes disturbing such aggregation will lead to an easy-to-quantify weakening of the signal. Based on this concept, a homogeneous aptamer-based assay for the detection of sulfadimethoxine (SDM) has been developed as a microfluidic CL flow-injection platform. Here, the efficient mixing of gold nanoparticles, aptamers, and analyte in short channel distances is of utmost importance, and two-dimensional (2D) and three-dimensional (3D) mixer designs made via Xurography were investigated. In the end, since 2D designs could not provide sufficient mixing, a laminated 3D 5-layer microfluidic mixer was developed and optimized with respect to mixing capability and observation by the charge-coupled device (CCD) camera. Furthermore, the performance of standard luminol and its more hydrophilic derivative m-carboxy luminol was studied identifying the hydrophilic derivative to provide tenfold more signal enhancement and reliable results. Finally, the novel detection platform was used for the specific detection of SDM via its aptamer and yielded a stunning dynamic range over 5 orders of magnitude (0.01–1000 ng/ml) and a limit of detection of 4 pg/ml. This new detection concept not only outperforms other methods for SDM detection, but can be suggested as a new flow-injection strategy for aptamer-based rapid and cost-efficient analysis in environmental monitoring and food safety.

COVID-19 diagnosis by SARS-CoV-2 Spike protein detection in saliva using an ultrasensitive magneto-assay based on disposable electrochemical sensor

The outbreak of the COVID-19 pandemic, caused by Severe Acute Respiratory Syndrome of Coronavirus 2 (SARS-CoV-2), has fueled the search for diagnostic tests aiming at the control and reduction of the viral transmission. The main technique used for diagnosing the Coronavirus disease (COVID-19) is the reverse transcription-polymerase chain reaction (RT-PCR) technique. However, considering the high number of cases and the underlying limitations of the RT-PCR technique, especially with regard to accessibility and cost of the test, one does not need to overemphasize the need to develop new and less expensive testing techniques that can aid the early diagnosis of the disease. With that in mind, we developed an ultrasensitive magneto-assay using magnetic beads and gold nanoparticles conjugated to human angiotensin-converting enzyme 2 (ACE2) peptide (Gln²⁴-Gln⁴²) for the capturing and detection of SARS-CoV-2 Spike protein in human saliva. The technique applied involved the use of a disposable electrochemical device containing eight screen-printed carbon electrodes which allow the simultaneous analysis of eight samples. The magneto-assay exhibited an ultralow limit of detection of 0.35 ag mL^-1 for the detection of SARS-CoV-2 Spike protein in saliva. The magneto-assay was tested in saliva samples from healthy and SARS-CoV-2-infected individuals. In terms of efficiency, the proposed technique - which presented a sensitivity of 100.0% and specificity of 93.7% for SARS-CoV-2 Spike protein-exhibited great similarity with the RT-PCR technique. The results obtained point to the application potential of this simple, low-cost magneto-assay for saliva-based point-of-care COVID-19 diagnosis.

Nanoscale Affinity Double Layer Overcomes the Poor Antimatrix Interference Capability of Aptamers

Poor antimatrix interference capability of aptamers is one of the major obstacles preventing their wide applications for real-sample detections. Here, we devise a multiple-function interface, denoted as a nanoscale affinity double layer (NADL), to overcome this bottleneck via in situ simultaneous target enrichment, purification, and detection. The NADL consists of an upper aptamer layer for target purification and sensing and a lower nanoscale solid-phase microextraction (SPME) layer for sample enrichment. The targets flowing through the NADL-functionalized surface are instantly million-fold enriched and purified by the sequential extraction of aptamer and SPME. The formation of the aptamer-target complex is greatly enhanced, enabling ultrasensitive detection of targets with minimized interference from the matrix. Taking the fiber-optic evanescent wave sensor as an example, we demonstrated the feasibility and generality of the NADL. The unprecedented detection of limits of 800, 4.8, 40, and 0.14 fM were, respectively, achieved for three representative small-molecule targets with distinct hydrophobicity (kanamycin A, sulfadimethoxine, and di-(2-ethylhexyl) phthalate) and protein target (human serum albumin), corresponding to 2500 to 3 × 10⁸-fold improvement compared to the sensors without the NADL. Our sensors also showed exceptionally high target specificity (>1000) and tunable dynamic ranges simply by manipulating the SPME layer. With these features comes the ability to directly detect targets in diluted environmental, food, and biological samples at concentrations all well below the tolerance limits.

Emergent Biosensing Technologies Based on Fluorescence Spectroscopy and Surface Plasmon Resonance

The purpose of this work is to provide an exhaustive overview of the emerging biosensor technologies for the detection of analytes of interest for food, environment, security, and health. Over the years, biosensors have acquired increasing importance in a wide range of applications due to synergistic studies of various scientific disciplines, determining their great commercial potential and revealing how nanotechnology and biotechnology can be strictly connected. In the present scenario, biosensors have increased their detection limit and sensitivity unthinkable until a few years ago. The most widely used biosensors are optical-based devices such as surface plasmon resonance (SPR)-based biosensors and fluorescence-based biosensors. Here, we will review them by highlighting how the progress in their design and development could impact our daily life.

Selection and truncation of aptamers for ultrasensitive detection of sulfamethazine using a fluorescent biosensor based on graphene oxide

We developed a fluorescent aptamer/graphene oxide (GO)-based biosensor to detect sulfamethazine (SMZ) residues in animal-derived foods. The SMZ-bound aptamers were identified and screened with an improved GO-SELEX technique using non-immobilizing ssDNA library. After seven rounds of selection, six SMZ aptamers were sequenced and analyzed for secondary structure, and their affinity and specificity were assessed by binding assays. The truncated aptamer (SMZ1S: 5'-CGTTAGACG-3') with a unique stem-loop structure showed the highest affinity (K_d = 24.6 nM) to SMZ and was used to develop a GO-based fluorescent aptasensor. The binding mechanism between SMZ1S and SMZ was further analyzed by molecular docking. Under optimal conditions, the fluorescent aptasensor showed low detection limits (0.35 ng/mL) and a wide dynamic linear range (from 2 to 100 ng/mL). The aptasensor was also validated against real samples spiked with SMZ, which showed a fluorescence recovery from 93.9 to 108.8% and a coefficient of variation of < 12.7%. Taken together, these results suggest that this novel aptasensor can be used to sensitively, selectively, and accurately detect SMZ residues in foods. Schematic illustration of fluorescent aptasensor based on aptamer/graphene oxide complex detection of of SMZ.

Determination of sulfadimethoxine in milk with aptamer-functionalized Fe3 O4 /graphene oxide as magnetic solid-phase extraction adsorbent prior to HPLC

An aptamer (Apt) functionalized magnetic material was prepared by covalently link Apt to Fe₃ O₄ /graphene oxide (Fe₃ O₄ /GO) composite by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide, and then characterized by FTIR spectroscopy, X-ray diffraction, and vibration sample magnetometry. The obtained composite of Fe₃ O₄ /GO/Apt was employed as magnetic solid-phase extraction adsorbent for the selective preconcentration of sulfadimethoxine prior to analysis by high-performance liquid chromatography. Under the optimal conditions (sample pH of 4.0, sorbent dosage of 20 mg, extraction time of 3 h, and methanol-5% acetic acid solution as eluent), a good linear relationship was obtained between the peak area and concentration of sulfadimethoxine in the range of 5.0 to 1500.0 µg/L with correlation coefficient of 0.9997. The limit of detection (S/N = 3) was 3.3 µg/L. The developed method was successfully applied to the analysis of sulfadimethoxine in milk with recoveries in the range of 75.9-92.3% and relative standard deviations less than 8.1%. The adsorption mechanism of Fe₃ O₄ /GO/Apt toward sulfadimethoxine was studied through the adsorption kinetics and adsorption isotherms, and the results show that the adsorption process fits well with the pseudo-second-order kinetic model and the adsorbate on Fe₃ O₄ /GO/Apt is multilayer and heterogeneous.

A Sensitive and Selective Electrochemical Sensor for Sulfadimethoxine Based on Electropolymerized Molecularly Imprinted Poly (o-aminophenol) Film

Background:

As a broad-spectrum antibiotic of the sulfonamide family, Sulfadimethoxine (SDM) has been widely utilized for therapeutic and growth-promoting purposes in animals. However, the use of SDM can cause residual problems. Even a low concentration of SDM in the aquatic system can exert toxic effects on target organisms and green algae. Therefore, the quantitation of SDM residues has become an important task.

Methods:

The present work describes the development of a sensitive and selective electrochemical sensor for sulfadimethoxine based on molecularly imprinted poly(o-aminophenol) film. The molecular imprinted polymer film was fabricated by electropolymerizing o-aminophenol in the presence of SDM after depositing carboxylfunctionalized multi-walled carbon nanotubes onto a glassy carbon electrode surface. SDM can be quickly removed by electrochemical methods. The imprinted polymer film was characterized by cyclic voltammetry, differential pulse voltammetry and scanning electron microscopy.

Results:

Under the selected optimal conditions, the molecularly imprinted sensor shows a linear range from 1.0 × 10-7 to 2.0 × 10-5 mol L-1 for SDM, with a detection limit of 4.0 × 10-8 mol L-1. The sensor was applied to the determination of SDM in aquaculture water samples successfully, with the recoveries ranging from 95% to 106%.

Conclusion:

The proposed sensor exhibited a high degree of selectivity for SDM in comparison to other structurally similar molecules, along with long-term stability, good reproducibility and excellent regeneration capacity. The sensor may offer a feasible strategy for the analysis of SDM in aquaculture water samples.

The Growing Interest in Development of Innovative Optical Aptasensors for the Detection of Antimicrobial Residues in Food Products

The presence of antimicrobial residues in food-producing animals can lead to harmful effects on the consumer (e.g., allergies, antimicrobial resistance, toxicological effects) and cause issues in food transformation (i.e., cheese, yogurts production). Therefore, to control antimicrobial residues in food products of animal origin, screening methods are of utmost importance. Microbiological and immunological methods (e.g., ELISA, dipsticks) are conventional screening methods. Biosensors are an innovative solution for the development of more performant screening methods. Among the different kinds of biosensing elements (e.g., antibodies, aptamers, molecularly imprinted polymers (MIP), enzymes), aptamers for targeting antimicrobial residues are in continuous development since 2000. Therefore, this review has highlighted recent advances in the development of aptasensors, which present multiple advantages over immunosensors. Most of the aptasensors described in the literature for the detection of antimicrobial residues in animal-derived food products are either optical or electrochemical sensors. In this review, I have focused on optical aptasensors and showed how nanotechnologies (nanomaterials, micro/nanofluidics, and signal amplification techniques) largely contribute to the improvement of their performance (sensitivity, specificity, miniaturization, portability). Finally, I have explored different techniques to develop multiplex screening methods. Multiplex screening methods are necessary for the wide spectrum detection of antimicrobials authorized for animal treatment (i.e., having maximum residue limits).

Universal Design of Structure-Switching Aptamers with Signal Reporting Functionality

Structure-switching aptamers (SSAs) offer a promising recognition element for sensor development. However, the generation of SSAs via in vitro aptamer selection technologies or postselection engineering is challenging. Inspired by the two-domain structure of antibodies, we have devised a simple, universal strategy for engineering aptamers into SSAs with signal reporting functionality. These constructs consist of a "constant" domain, comprising a split DNAzyme G-quadruplex (G4) region for signal transduction, and a "variable" domain, comprising an aptamer sequence capable of specific target binding. In the absence of target, the G4-SSA construct folds into a parallel G4 structure with high peroxidase catalytic activity. Target binding disrupts the G4 structure, resulting in low enzymatic activity. We demonstrate that this change in DNAzyme activity enables sensitive and specific colorimetric detection of diverse targets including Hg²⁺, thrombin, sulfadimethoxine, cocaine, and 17β-estradiol. G4-SSAs can also achieve label-free fluorescence detection of various targets using a specific G4-binding dye. We demonstrate that diverse aptamers can be readily engineered into G4-SSA constructs independent of target class, binding affinity, aptamer length, or structure. This design strategy could broadly extend the power, accessibility, and utility of numerous SSA-based biosensors.

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 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 the detection limits of 3.41 ng mL^-1 for water and 4.41 ng g^-1 for fish samples (3σ, n = 9).

Electrochemical aptasensor for sulfadimethoxine detection based on the triggered cleavage activity of nuclease P1 by aptamer-target complex

Herein, a simple and selective electrochemical method was developed for sulfadimethoxine detection based on the triggered cleavage activity of nuclease P1 by the formation of aptamer and sulfadimethoxine conjugate. After probe DNA was immobilized on gold electrode surface, aptamer DNA labeled with biotin at its 5'-terminal was then captured on electrode surface through the hybridization reaction between probe DNA and aptamer DNA. The formed double-stranded DNA (dsDNA) can block the digestion activity of Nuclease P1 towards the single-stranded probe DNA. Then, the anti-dsDNA antibody was further modified on electrode surface based on the specific interaction between dsDNA and antibody. Due to the electrostatic repulsion effect and steric-hindrance effect, a weak electrochemical signal was obtained at this electrode. However, in the presence of sulfadimethoxine, it can interact with aptamer DNA, and then the formation of dsDNA can be blocked. As a result, the probe DNA at its single-strand state can be digested by Nuclease P1, which leads to the failure of the immobilization of anti-dsDNA antibody. At this state, a strong electrochemical signal was obtained. Based on the change of the electrochemical signal, sulfadimethoxine can be detected with linear range of 0.1-500 nmol/L. The detection limit was 0.038 nmol/L. The developed method possesses high detection selectivity and sensitivity. The applicability of this method was also proved by detecting sulfadimethoxine in veterinary drug and milk with satisfactory results.

Aptasensor for multiplex detection of antibiotics based on FRET strategy combined with aptamer/graphene oxide complex

The development of a multiplexed sensing platform is necessary for highly selective, sensitive, and rapid screening of specific antibiotics. In this study, we designed a novel multiplex aptasensor for antibiotics by fluorescence resonance energy transfer (FRET) strategy using DNase I-assisted cyclic enzymatic signal amplification (CESA) method combined with aptamer/graphene oxide complex. The aptamers specific for sulfadimethoxine, kanamycin, and ampicillin were conjugated with Cyanine 3 (Cy3), 6-Carboxyfluorescein (FAM), and Cyanine 5 (Cy5), respectively, and graphene oxide (GO) was adopted to quench the fluorescence of the three different fluorophores with the efficiencies of 94.36%, 93.94%, and 96.97% for Cy3, FAM, and Cy5, respectively. CESA method was used for sensitive detection, resulting in a 2.1-fold increased signal compared to those of unamplified method. The aptasensor rapidly detected antibiotics in solution with limit of detection of 1.997, 2.664, and 2.337 ng/mL for sulfadimethoxine, kanamycin, and ampicillin, respectively. In addition, antibiotics dissolved in milk were efficiently detected with similar sensitivities. Multiplexed detection test proved that the fluorescently modified aptamers could work separately from each other. The results indicate that the aptasensor offers high specificity for each antibiotic and enables simultaneous and multicolor sensing for rapid screening of multiple antibiotics at the same time.

Label-Free Fluorescence-Based Aptasensor for the Detection of Sulfadimethoxine in Water and Fish

Fluorescence-based aptasensors possess high sensitivity but are complicated and usually require multistep labeling and modification in method design, which severely limit the practical applications. Here, a label-free fluorescence-based aptasensor, consisting of aptamer, gold nanoparticles (AuNPs), and cadmium telluride (CdTe) quantum dots (QDs), was developed for the detection of sulfadimethoxine (SDM) in water and fish based on the specific recognition of SDM-aptamer and the inner filter effect of QDs and AuNPs. In the absence of a target, AuNPs dispersed in salt solution because of the aptamer protection, which could effectively quench the fluorescence emission of QDs, while in the presence of SDM, AuNPs aggregated due to the specific recognition of SDM-aptamer to SDM, which resulted in fluorescence recovery. A linear response of SDM concentrations in the range of 10-250 ng mL^-1 ( R²= 0.99) was obtained, and the detection limit was 1.54 ng mL^-1 (3σ, n = 9), far below the maximum residue limit (100 ng mL^-1) of SDM in edible animal tissues regulated by China and the European Commission. The fluorescence-based aptasensor was applied to the detection of SDM in aquaculture water and fish samples with high accuracy, excellent precision, and ideal selectivity. The results indicated that the developed aptasensor was simple in design, easy to operate, and could be used to detect rapidly and accurately SDM in water and fish samples.

Electrospun Nanobelt-Shaped Polymer Membranes for Fast and High-Sensitivity Detection of Metal Ions

Until now, no polymer nanobelt-shaped materials have been developed as electrochemical, optical, and mass sensors. In this work, we first develop polymer nanobelt-shaped membranes for fast and high-sensitivity detection of metal ions, which are fabricated by a new nanobelt-based processing method with simultaneous zein matrix cross-linking and curcumin cross-linking. Their morphologies, optimal detection pH, ion selectivity, and ion detection sensitivity are systematically analyzed. The limits of detection of electrospun curcumin-loaded zein membranes with a detection time of 0.5 h are as follows: cross-linked nanobelt-shaped membranes (0.3 mg/L) < uncross-linked nanobelt-shaped membranes (1 mg/L) ≈ cross-linked nanofibrous membranes (1 mg/L) < uncross-linked nanofibrous membranes (3 mg/L). The cross-linked nanobelt-shaped membranes are also applied to detect Fe³⁺ in drinking water and environmental water. Finally, the mechanisms of Fe³⁺ detection by these membranes are studied and discussed. The results demonstrate that the difference of limit of detection is dependent on if the curcumin sensor is cross-linked or not and the membrane nanostructures (nanobelts or nanofibers). Cross-linking produces stable sensor molecules on the surface and therefore induces low limits of detection. Compared with nanofibers, nanobelts have a higher surface-to-volume ratio and can have more sensor molecules on their surfaces and therefore have lower limits of detection. In addition, the as-prepared membranes had good membrane storage stability (at least 3 months at room temperature). All of these results suggest that cross-linked electrospun nanobelt-shaped membranes by a new nanobelt-based processing method are ideal platforms for sensing. We believe that they will attract increasing attention in scientific and engineering fields such as materials, environmental, and food science.

Design and construction of Z-scheme Bi2S3/nitrogen-doped graphene quantum dots: Boosted photoelectric conversion efficiency for high-performance photoelectrochemical aptasensing of sulfadimethoxine

Rational design and fabrication of Z-scheme visible-light-driven photoactive materials have drawn much attention owing to their great potential in handling environment and energy crisis. In this work, Z-scheme Bi₂S₃/nitrogen-doped graphene quantum dots (NGQDs) with superior photoelectric conversion efficiency were designed and fabricated, which demonstrated enhanced photoactivity compared with Bi₂S₃ owing to the improved separation efficiency of photogenerated electron and hole pairs. The emphasis was put on designing Z-scheme Bi₂S₃/NGQDs, and then the mechanism of Z-scheme charge transfer mode was verified by the electron spin resonance (ESR) technique. On this basis, the proposed sensor exhibited a wide linear range of 0.1-120 nM and a detection limit of 0.03 nM (S/N = 3) for SDM, with high sensitivity (0.075 μA nM ^-1), good selectivity and stability. Moreover, the proposed PEC aptasensor using Bi₂S₃/NGQDs as the photoelectrode achieved sensitive and selective determination of sulfadimethoxine in milk samples. This work could provide some ideas for designing other Z-scheme photoactive species and insights into the charge transfer mechanism of Z-scheme. Furthermore, the promising applicability of PEC aptasensor using photoactive species could be extended to other accurate monitoring for contaminants.

Recent developments of photoelectrochemical biosensors for food analysis

Recent developments of photoelectrochemical biosensors for food analysis are summarized and the future prospects in this field are discussed.

Voltammetric aptasensor for sulfadimethoxine using a nanohybrid composed of multifunctional fullerene, reduced graphene oxide and Pt@Au nanoparticles, and based on direct electron transfer to the active site of glucose oxidase

This work describes a voltammetric and ultrasensitive aptasensor for sulfadimethoxine (SDM). It is based on signal amplification by making use of a multifunctional fullerene-doped reduced graphene oxide nanohybrid. The nanohybrid was coated with poly(diallyldimethylammonium chloride) to obtain a material (P-C₆₀-rGO) with large specific surface area and a unique adsorption ability for loading it with glucose oxidase (GOx). The coating also facilitates the direct electron transfer between the active site of GOx and the glassy carbon electrode (GCE). The P-C₆₀-rGO were then modified with Pt@Au nanoparticles, and the thiolated SDM-binding aptamer was immobilized on the nanoparticles. On exposure of the modified GCE to a solution containing SDM, it binds to the aptamer. The results were recorded through the signal responses generated from the redox center of GOx (FAD/FADH₂) by cyclic voltammetry at a scan rate of 100 mV·s^-1 from -0.25 to -0.65 V. Accordingly, The sensor has good specificity and stability, and response is linear in the 10 fg·mL^-1 to 50 ng·mL^-1 SDM concentration range with a detection limit of 8.7 fg·mL^-1. Graphical abstract Schematic presentation of an electrochemical aptasensor for sulfadimethoxine (SDM) using multifunctional fullerene-doped graphene (C₆₀-rGO) nanohybrids for amplification. The limit of detection for SDM is as low as 8.7 fg·mL^-1.

Critical Review: DNA Aptasensors, Are They Ready for Monitoring Organic Pollutants in Natural and Treated Water Sources?

There is a growing need to monitor anthropogenic organic contaminants detected in water sources. DNA aptamers are synthetic single-stranded oligonucleotides, selected to bind to target contaminants with favorable selectivity and sensitivity. These aptamers can be functionalized and are used with a variety of sensing platforms to develop sensors, or aptasensors. In this critical review, we (1) identify the state-of-the-art in DNA aptamer selection, (2) evaluate target and aptamer properties that make for sensitive and selective binding and sensing, (3) determine strengths and weaknesses of alternative sensing platforms, and (4) assess the potential for aptasensors to quantify environmentally relevant concentrations of organic contaminants in water. Among a suite of target and aptamer properties, binding affinity is either directly (e.g., organic carbon partition coefficient) or inversely (e.g., polar surface area) correlated to properties that indicate greater target hydrophobicity results in the strongest binding aptamers, and binding affinity is correlated to aptasensor limits of detection. Electrochemical-based aptasensors show the greatest sensitivity, which is similar to ELISA-based methods. Only a handful of aptasensors can detect organic pollutants at environmentally relevant concentrations, and interference from structurally similar analogs commonly present in natural waters is a yet-to-be overcome challenge. These findings lead to recommendations to improve aptasensor performance.

Aptamer-Based Biosensors for Antibiotic Detection: A Review

Antibiotic resistance and, accordingly, their pollution because of uncontrolled usage has emerged as a serious problem in recent years. Hence, there is an increased demand to develop robust, easy, and sensitive methods for rapid evaluation of antibiotics and their residues. Among different analytical methods, the aptamer-based biosensors (aptasensors) have attracted considerable attention because of good selectivity, specificity, and sensitivity. This review gives an overview about recently-developed aptasensors for antibiotic detection. The use of various aptamer assays to determine different groups of antibiotics, like β-lactams, aminoglycosides, anthracyclines, chloramphenicol, (fluoro)quinolones, lincosamide, tetracyclines, and sulfonamides are presented in this paper.

Practical Application of Aptamer-Based Biosensors in Detection of Low Molecular Weight Pollutants in Water Sources

Water pollution has become one of the leading causes of human health problems. Low molecular weight pollutants, even at trace concentrations in water sources, have aroused global attention due to their toxicity after long-time exposure. There is an increased demand for appropriate methods to detect these pollutants in aquatic systems. Aptamers, single-stranded DNA or RNA, have high affinity and specificity to each of their target molecule, similar to antigen-antibody interaction. Aptamers can be selected using a method called Systematic Evolution of Ligands by EXponential enrichment (SELEX). Recent years we have witnessed great progress in developing aptamer selection and aptamer-based sensors for low molecular weight pollutants in water sources, such as tap water, seawater, lake water, river water, as well as wastewater and its effluents. This review provides an overview of aptamer-based methods as a novel approach for detecting low molecular weight pollutants in water sources.