Label-free photoelectrochemical aptasensor for tetracycline detection based on cerium doped CdS sensitized BiYWO6

A photoelectrochemical aptasensor based on double Z-scheme α-Fe2O3/MoS2/Bi2S3 ternary heterojunction for sensitive detection of circulating tumor cells

A novel photoelectrochemical (PEC) aptasensor based on a dual Z-scheme α-Fe2O3/MoS2/Bi2S3 ternary heterojunction for the ultrasensitive detection of circulating tumor cells (CTCs) was developed. The α-Fe2O3/MoS2/Bi2S3 nanocomposite was prepared via a step-by-step route, and the photoproduced electron/hole transfer path was speculated by conducting trapping experiments of reactive species. α-Fe2O3/MoS2/Bi2S3-modified electrodes exhibited greatly enhanced photocurrent under visible light due to the double Z-scheme charge transfer process, which met the requirement of the PEC sensor for detecting larger targets. After the aptamer was conjugated on the photoelectrode through chitosan (CS) and glutaraldehyde (GA), when MCF-7 cells were presented and captured, the photocurrent of the PEC biosensing system decreased due to steric hindrance. The current intensity had a linear relationship with the logarithm of MCF-7 cell concentration ranging from 10 to 1×105 cells mL-1, with a low detection limit of 3 cell mL-1 (S/N = 3). The dual Z-scheme α-Fe2O3/MoS2/Bi2S3 ternary heterojunction-modified PEC aptasensor exhibited high sensitivity and excellent specificity and stability. Additionally, MCF-7 cells in human serum were determined by this PEC aptasensor, exhibiting great potential as a promising tool for clinical detection.

Ultrasensitive electrochemical detection of amyloid-beta oligomers using double amplification strategy by MXene substrate and covalent organic framework-based probe

Most of the existing electrochemical systems failed to achieve satisfactory results in early diagnosis of Alzheimer's disease (AD) owing to a deficiency of effective signal transduction. A new method for the electrochemical detection of AD biomarkers (amyloid-beta oligomers, Aβ1-42 oligomers) was developed based on a double amplification strategy. Titanium carbide (Ti3C2) MXene decorated by gold nanoparticles (Au-MXene) as the electrode substrate not only gave rise to the electrochemical response due to its paradoxical surface area and conspicuous charge mobility, but also provided vast numbers of binding sites for aptamers (Apt) of Aβ1-42 oligomers. Meanwhile, AuNPs were incorporated into covalent organic frameworks (COFs), which were further modified by Apt and electron mediator (toluidine blue, TB). The Apt/TB-Au@COFs composite was utilized as a label because of their improvement of the electron-hole separation efficiency and optimization of the charge-carrier utilization. The proposed electrochemical assay established highly efficient platform for the detection of Aβ1-42 oligomers with a linear range from 0.01 pg mL-1 to 180 pg mL-1 and an ultralow detection limit of 4.27 fg mL-1 (S/N = 3). This biosensing platform had potential applications in molecular diagnostics of AD serum samples.

Label-free electrochemical cancer cell detection leveraging hemoglobin-encapsulated silver nanoclusters and Cu-MOF nanohybrids on a graphene-assisted dual-modal probe

Breast cancer detection at an early stage significantly increases the chances of successful treatment and survival. This study presents an electrochemical biosensor for detecting breast cancer cells, utilizing silver nanoclusters encapsulated by hemoglobin and Cu (II)-porphyrin-metal organic framework (BioMOF) in a graphene-incorporated nanohybrid probe. This Hb-AgNCs@MOF-G probe demonstrates high electrochemical activity, superior dispersity, porosity, and a large surface area for effective functionalization. Using a green ultrasonic-assisted stirring method, we fabricate ultra-small 5 nm particles that readily immobilize on a glassy carbon electrode, generating a detection signal when interacting with ferricyanide/ferrocyanide redox probes. The resulting immunosensor detects as few as 2 cells/mL using Electrochemical Impedance Spectroscopy (EIS) "signal on" and 16 cells/mL via Square Wave Voltammetry (SWV) "signal off", within a broad range of cell concentrations (102-5 × 104 cells/mL). Our designed sensor shows improved selectivity (5- to 16-fold) and robust detection in human blood with a recovery efficiency between 94.8-106% (EIS method) and 95.4-111% (SWV method). This sensor could streamline early cancer diagnosis and monitor patient treatment without requiring labelling or signal amplification. As a pioneering endeavor, we've utilized integrated porous MOFs with Hb-encapsulated silver nanoclusters in cancer detection, where these components collectively enhance the overall functionality.

Conductive phthalocyanine-based porous organic polymer as sensing platform for rapid determination of vanillin

Vanillin (Van) is widely utilized in processed foods and medicines for its appealing scent and multiple therapeutic benefits. However, its overconsumption poses a risk to public health, making its quantification essential for ensuring food and medicine safety and quality. This study introduces a stable and conductive phthalocyanine-based porous organic polymer (NiPc-CC POP), synthesized through a straightforward electrophilic substitution of nickel tetra-amine phthalocyanine (NiTAPc) with cyanuric chloride (CC). Appropriate characterization techniques were employed to determine the morphologies and structures of the synthesized materials. Furthermore, the NiPc-CC POP was applied to devise a sensitive Van detection method. Leveraging the high electrocatalytic activity of NiPc-CC POP toward Van oxidation, a linear response of 0.15-32 μmol L-1 was achieved, along with an exceptional detection limit of 0.10 μmol L-1. The sensor demonstrated high selectivity and stability. Samples of human serum and tablets spiked with Van were analyzed, yielding satisfactory recoveries. Consequently, this work contributes to the advancement of sensitive detection platforms for Van at minimal concentrations.

Optical sensing of tetracycline concentration using a liquid crystal-based platform targeting the chelating properties of tetracycline

In this study, a liquid crystal (LC)-based assay for the real-time detection of tetracycline (Tc) was developed. The sensor was constructed by implementing an LC-based platform that utilized the chelating properties of Tc to target Tc metal ions. This design enabled Tc-dependent induction of changes in the optical image of the LC; these modifications could then be observed in real-time with the naked eye. The performance of the sensor in detecting Tc was investigated with various metal ions to identify the most effective metal ion for Tc detection. In addition, the selectivity of the sensor was evaluated using different antibiotics. A correlation between Tc concentration and the optical intensity of the LC optical images was established, which enabled the quantification of Tc concentrations. The proposed method can detect Tc concentrations with a detection limit as low as 2.67 pM. Tests were conducted on milk, honey, and serum samples, which demonstrated that the proposed assay is highly accurate and reliable. The high sensitivity and selectivity of the proposed method make it a promising tool for real-time Tc detection, with potential applications in fields ranging from biomedical research to agriculture.

Recent advances in luminescence and aptamer sensors based analytical determination, adsorptive removal, degradation of the tetracycline antibiotics, an overview and outlook

Tetracycline antibiotics (TCs), one of the important antibiotic groups, have been widely used in human and veterinary medicines. Their residues in foodstuff, soil and sewage have caused serious threats to food safety, ecological environment and human health. Here, we reviewed the potential harms of TCs residues to foodstuff, environment and human beings, discussed the luminescence and aptamer sensors based analytical determination, adsorptive removal, and degradation strategies of TCs residues from a recent 5-year period. The advantages and intrinsic limitations of these strategies have been compared and discussed, the potential challenges and opportunities in TCs residues degradation have also been deliberated and explored.

Advancements in nanomaterial-based aptasensors for the detection of emerging organic pollutants in environmental and biological samples

The combination of nanomaterials (NMs) and aptamers into aptasensors enables highly specific and sensitive detection of diverse pollutants. The great potential of aptasensors is recognized for the detection of diverse emerging organic pollutants (EOPs) in different environmental and biological matrices. In addition to high sensitivity and selectivity, NM-based aptasensors have many other advantages such as portability, miniaturization, facile use, and affordability. This work showcases the recent advances achieved in the design and fabrication of NM-based aptasensors for monitoring EOPs (e.g., hormones, phenolic contaminants, pesticides, and pharmaceuticals). On the basis of their sensing mechanisms, the covered aptasensing systems are classified as electrochemical, colorimetric, PEC, fluorescence, SERS, and ECL. Special attention has been paid to the fabrication processes, analytical achievements, and sensing mechanisms of NM-based aptasensors. Further, the practical utility of aptasensing approaches has also been assessed based on their basic performance metrics (e.g., detection limits, sensing ranges, and response times).

A self-powered photoelectrochemical oxytetracycline aptasensor: An integrated heterojunction photoanode of metal-organic framework derived ZnO nanopolyhedra/graphitic carbon nitride with high carrier density

The development of effective strategies for the detection of oxytetracycline (OTC) in soil is of great importance for preserving agri-environmental safety and human health. Herein, a novel photoactive material of metal-organic framework (MOF) derived ZnO nanopolyhedra/graphitic carbon nitride (ZnO/g-C3N4) heterojunction was designed by mixing calcination of zeolite imidazole framework-8 (ZIF-8) and melamine. A self-powered photoelectrochemical aptasensor for the sensitive and selective detection of OTC in soil was proposed using ZnO/g-C3N4 as the photoanode. The photoactivity of the MOF derived ZnO nanopolyhedra was regulated effectively by the introduction of g-C3N4, which resulted in a 7-fold increase in the photocurrent of the ZnO nanopolyhedra at a bias potential of 0 V. It was assigned to the higher carrier density of ZnO/g-C3N4. By virtue of the amplified photocurrent of ZnO/g-C3N4, the specificity of the OTC aptamer and the anti-interference ability of the self-powered sensing method, the designed aptasensor demonstrated the advantages of a wide linear range (0.005-200 nM), low limit of detection (1.49 × 10-3 nM), good selectivity and good reproducibility. For real soil sample analysis, satisfactory recoveries were obtained and further verified by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS).

Construction of direct Z-scheme g-C3N4/BiYWO6 heterojunction photocatalyst with enhanced visible light activity towards the degradation of methylene blue

Construction of the Z-scheme heterojunction photocatalyst achieved highly improved photocatalytic ability by its high redox ability of the photoinduced e^--h⁺ pairs. In the study, Z-scheme g-C₃N₄/BiYWO₆ heterojunction photocatalyst is prepared by the single-step hydrothermal method. Further, its photocatalytic ability was assessed by degrading methylene blue under visible light exposure. Particularly, the optimized 30 wt% of g-C₃N₄ in the g-C₃N₄/BiYWO₆ composite exposes almost complete degradation after 90 min, that is ~ 3.0 times greater than the bare BiYWO₆ and g-C₃N₄ with the rate constant value 0.032 min^-1. Experimentally, the radical trapping studies indicate O₂·^- and ·OH radicals are playing a vital role in the photocatalytic degradation process. Also, the Z-scheme g-C₃N₄/BiYWO₆ heterojunction photocatalyst exhibits excellent photoelectrochemical property and it is stable after 5 cycles, which indicates its good reusability nature. These enhancements are due to the newly formed heterostructure that facilitates the migration and separation efficiency of the photoproduced e^--h⁺ pairs. Hence, the synthesized Z-scheme g-C₃N₄/BiYWO₆ heterostructure could be an excellent material for wastewater remediation works.

Selective Antibody-Free Sensing Membranes for Picogram Tetracycline Detection

As an antibody-free sensing membrane for the detection of the antibiotic tetracycline (TC), a liquid PVC membrane doped with the ion-pair tetracycline/θ-shaped anion [3,3'-Co(1,2-C2B9H11)2]- ([o-COSAN]-) was formulated and deposited on a SWCNT modified gold microelectrode. The chosen transduction technique was electrochemical impedance spectroscopy (EIS). The PVC membrane was composed of: the tetracycline/[o-COSAN]- ion-pair, a plasticizer. A detection limit of 0.3 pg/L was obtained with this membrane, using bis(2-ethylhexyl) sebacate as a plasticizer. The sensitivity of detection of tetracycline was five times higher than that of oxytetracycline and of terramycin, and 22 times higher than that of demeclocycline. A shelf-life of the prepared sensor was more than six months and was used for detection in spiked honey samples. These results open the way to having continuous monitoring sensors with a high detection capacity, are easy to clean, avoid the use of antibodies, and produce a direct measurement.

A Sensitive Photoelectrochemical Sensor for Levodopa Detection Using Benzothiadiazole-Based Conjugated Microporous Polymer-Coated Graphene Heterostructures

Since the 1960s, levodopa (LDA) has been the standard drug for treating of Parkinson's disease. In this study, a novel benzothiadiazole-based conjugated microporous polymer-coated graphene heterostructure (CMP-rGO) was synthesized and used to construct a sensitive photoelectrochemical (PEC) sensor capable of detecting LDA. Under optimal experimental conditions, the intensity of the photocurrent produced by the sensor was linear from 0.005 to 40 μM, and the limit of detection of the sensor was 0.0027 μM. The sensor showed good repeatability, stability, and selectivity for LDA detection. Finally, the constructed sensor was used to detect LDA in levodopa tablets, human serum samples, and urine samples and satisfactory results were obtained. Therefore, the PEC sensor provides a novel platform for the detection of LDA in real samples and broadens the applications of conjugated microporous polymers in PEC sensing.

A novel metal-organic frameworks composite-based label-free point-of-care quartz crystal microbalance aptasensing platform for tetracycline detection

A novel label-free point-of-care quartz crystal microbalance (QCM) aptasensing platform based on metal-organic frameworks (MOFs) and gold nanoparticles (AuNPs) was fabricated for tetracycline (TC) detection. MOFs (HKUST-1) and AuNPs were modified onto the sensing interface of QCM sensor to enhance the sensing performance of the QCM aptasensor. TC aptamer with sulfhydryl group was fixed through Au-S bond. The recognition performance of the aptasensor was predicted and verified by the computer simulation. At the optimal conditions, the frequency change of the sensor was adopted for quantitative detection of TC. The prepared QCM aptasensor exhibited a wide linear range from 1 × 10^-10 g mL^-1 to 1 × 10^-5 g mL^-1 with low limit of detection (0.8 × 10^-11 g mL^-1). High sensitivity, good selectivity, acceptable recoveries (87.6-91.4%) in real samples were obtained. For the first time, MOFs were utilized in the construction of QCM aptasensing platform, providing a promising application way of MOFs in the QCM sensing.

One-pot synthesis of bismuth yttrium tungstate nanosheet decorated 3D-BiOBr nanoflower heterostructure with enhanced visible light photocatalytic activity

A visible light driven BiOBr/Bi_xY_1-xWO₆ nanocomposite photocatalyst of various compositions are prepared by the addition of different amounts of KBr (0.5, 1.0, 1.5, 2.0 mmol) in Bi_xY_1-xWO₆ by a one-pot hydrothermal method. Furthermore, the photocatalytic properties of the as-prepared materials are analyzed by the decomposition of methylene blue under visible light illumination. In particular, the BiOBr/Bi_xY_1-xWO₆ nanocomposite prepared by taking 1.5 mmol of KBr present a superior photocatalytic ability (78.3%) with the rate constant value 0.016 min^-1, a low bandgap (E_g = 2.51 eV) as well as photoluminescence emission intensity than other photocatalysts prepared in this study. The radical scavenging studies revealed that OH and h⁺ performed an imperative role in the decomposition of methylene blue. Furthermore, the optimized photocatalyst is stable even after four cycles, which exposes the excellent photostability and reusability properties of the photocatalyst. In addition, a plausible mechanism of decomposition of methylene blue under visible light irradiation is also proposed.

Tellurium-based chemical sensors

The various tellurium-based chemical sensors are described. This article focuses on four types of Tellurium sensors such as CdTe quantum dots-based sensor, Te thin films-based sensor, Te nanostructures or nanoparticles-based sensor, and TeO2-based sensor.

Multiplex optical bioassays for food safety analysis: Toward on-site detection

Food safety analysis plays a significant role in controlling food contamination and supervision. In recent years, multiplex optical bioassays (MOBAs) have been widely applied to analyze multiple hazards due to their efficiency and low cost. However, due to the challenges such as multiplexing capacity, poor sensitivity, and bulky instrumentation, the further application of traditional MOBAs in food screening has been limited. In this review, effective strategies regarding food safety MOBAs are summarized, such as spatial-resolution modes performed in multi-T lines/dots strips or arrays of strip/microplate/microfluidic chip/SPR chip and signal-resolution modes employing distinguishable colorimetric/luminescence/fluorescence/surface plasma resonance/surface-enhanced Raman spectrum as signal tags. Following this, new trends on how to design engineered sensor architecture and exploit distinguishable signal reporters, how to improve both multiplexing capacity and sensitivity, and how to integrate these formats into smartphones so as to be mobile are summarized systematically. Typically, in the case of enhancing multiplexing capacity and detection throughput, microfluidic array chips with multichannel architecture would be a favorable approach to overcome the spatial and physical limitations of immunochromatographic assay (ICA) test strips. Moreover, noble metal nanoparticles and single-excitation, multiple-emission luminescence nanomaterials hold great potential in developing ultrasensitive MOBAs. Finally, the exploitation of innovative multiplexing strategy hybridized with powerful and widely available smartphones opens new perspectives to MOBAs. In future, the MOBAs should be more sensitive, have higher multiplexing capacity, and easier instrumentation.

Homogeneous Photoelectrochemical Aptasensors for Tetracycline Based on Sulfur-Doped g-C3N4/n-GaN Heterostructures Formed through Self-Assembly

The complex synthesis of photoelectric materials and the difficulty of fixing the identification elements on the photoelectrode are long-standing problems in the field of photoelectrochemical (PEC) biosensing. In this work, a simple PEC aptasensor construction strategy based on a sulfur-doped g-C₃N₄ (SCN)/n-GaN heterostructure photoelectrode was proposed. The SCN/n-GaN heterostructure can be formed through self-assembly in solution since SCN can be uniformly dispersed in solution. In addition, as a dual-function mediate, an aptamer can be fixed on an SCN substrate automatically because of the good adsorption performance of SCN. Therefore, tedious steps of PEC electrode preparation and the fixing of recognition elements were both avoided. Compared with the traditional ones, the construction difficulty and time cost of the prepared PEC aptasensors are greatly reduced. The simplified experimental process improves the stability and reproducibility of the aptasensor. Finally, tetracycline (TET) was used as a model target to verify the sensing performance of the proposed PEC strategy. TET can consume the photogenerated holes of the SCN/n-GaN heterostructure, promote carrier migration, and result in the change in the photocurrent. The linear relationship between the change in the photocurrent intensity and the TET concentration can be used to detect TET. The aptasensor has a linear range of 0.10-10.0 nmol L^-1 and the detection limit is 0.030 nmol L^-1 (3S/N). The aptasensor was applied to the detection of TET in milk samples with satisfactory results.

Heteroatom-free conjugated tetraphenylethylene polymers for selectively fluorescent detection of tetracycline

The antibiotic tetracycline (Tc) is a major contaminant in food and water, with adverse effects on both ecosystems and human health. The development of novel sensors for tetracycline detection is of great importance. In this work, we develop a novel heteroatom-free conjugated tetraphenylethylene polymer (TPE-CMP) fluorescence sensor for the detection of tetracycline. In the presence of Tc, the emission fluorescence of TPE-CMP was quenched by the photoinduced electron transfer mechanism to achieve high sensitivity. The polymers can detect tetracycline at a concentration of 0-100 μg/mL with a good linear correlation (0.99), and the limit of detection (LOD) is 1.23 μg/mL. Furthermore, TPE-CMP has excellent selectivity in detecting Tc in the presence of various anti-interference analytes, including ions and antibiotics. In addition, the practical feasibilities of TPE-CMP for Tc sensing were further investigated in milk, urine and wastewater samples with satisfactory recoveries (from 94.96% to 112.53% for milk, from 96.41% to 99.31% for urine and from 98.54% to 100.52% for wastewater). We have designed and synthesized TPE-CMP based on heteroatom-free for the specific fluorescence detection of tetracycline, expanding the range of fluorescence detection sensors and offering great promise for practical applications.

A sandwiched photoelectrochemical biosensing platform for detecting Cytokeratin-19 fragments based on Ag2S-sensitized BiOI/Bi2S3 heterostructure amplified by sulfur and nitrogen co-doped carbon quantum dots

A sandwiched photoelectrochemical (PEC) immunosensor based on BiOI/Bi₂S₃/Ag₂S was designed for the quantitative detection of cytokeratin-19 fragments (CYFRA21-1) in serum. In this work, due to the intervention of the narrow band gap Bi₂S₃, the absorption of the light source by the BiOI/Bi₂S₃ heterostructure has been significantly enhanced. Meanwhile, the matched band structure of BiOI, Bi₂S₃ and Ag₂S promoted the rapid transfer of electrons between the conduction bands and effectively inhibited the recombination of electron-hole pairs, thus enhanced the photoelectric signals. Sulfur and nitrogen co-doped carbon quantum dots (S,N-CQDs) with up-conversion luminescence properties provided more light energy for the base materials. On the other hand, S,N-CQDs were combined with Ab₂ through polydopamine (PDA), as secondary antibody labels, further enhanced the sensitivity of the sensor. Herein, the linear range of the sensor was from 0.001 to 100 ng mL^-1 and the detection limit was 1.72 pg mL^-1. In addition, the sensor provides a feasible way for the detection of tumor markers due to its excellent selectivity, repeatability and good stability.

[Ru(bpy)3]2+@Ce-UiO-66/Mn:Bi2S3 Heterojunction and Its Exceptional Photoelectrochemical Aptasensing Properties for Ofloxacin Detection

A photoelectrochemical (PEC) aptasensor on basis of [Ru(bpy)₃]²⁺@Ce-UiO-66/Mn:Bi₂S₃ composites was constructed for detecting ofloxacin (OFL). First, Ce-UiO-66, prepared by a solvothermal method, had Zr⁴⁺-Zr³⁺ and Ce⁴⁺-Ce³⁺ intervalence cycles to increase the charge separation efficiency. Subsequently, Ce-UiO-66 was further modified by [Ru(bpy)₃]²⁺ and Mn:Bi₂S₃ cosensitization to improve the photoelectric activity. [Ru(bpy)₃]²⁺ not only broadened the range of light absorbed but also reacted with an electron donor to maintain the photoelectric conversion process. Among the [Ru(bpy)₃]²⁺@Ce-UiO-66/Mn:Bi₂S₃ heterojunction, Mn:Bi₂S₃ was a photosensitizer, which maximized the efficiency of the electron-hole separation and significantly improved photocurrent. Then, an aptamer was used as a biorecognition unit for OFL-specific detection. Under the best conditions, the PEC aptasensor realized the sensitive detection of OFL, with a detection range of 0.01-100 nmol/L and a detection limit of 6 pmol/L. In addition, the constructed PEC OFL sensor showed good reproducibility, stability, and specificity.

Tetracycline Antibiotics: Elucidating the Electrochemical Fingerprint and Oxidation Pathway

Herein, a complete study of the electrochemical behavior of the most commonly used tetracycline antibiotics (TCs) on unmodified carbon screen-printed electrodes (SPEs) is presented. In addition, the oxidation pathway of TCs on SPE is elucidated, for the first time, with liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS). Square wave voltammetry (SWV) was used to study the electrochemical fingerprint (EF) of the antibiotics shaping the different oxidation processes of the TCs in a pH range from 2 to 12. Their characteristic structure and subsequent EF offer the possibility of distinguishing this class of antibiotics from other types. Under the optimized parameters, calibration curves of tetracycline (TET), doxycycline (DOXY), oxytetracycline (OXY), and chlortetracycline (CHL) in a Britton Robinson buffer solution (pH 9) exhibited a linear range between 5 and 100 µM with excellent reproducibilities (RSDTET = 3.01%, RSDDOXY = 3.29%, RSDOXY = 9.78% and RSDCHL = 6.88% at 10 µM, N = 3) and limits of detection (LOD) of LODTET = 4.15 µM, LODDOXY = 2.14 µM, LODOXY = 3.07 µM and LODCHL = 4.15 µM. Furthermore, binary, tertiary, and complex mixtures of all TCs were analyzed with SWV to investigate the corresponding EF. A dual pH screening (pH 4 and pH 9), together with the use of a custom-made Matlab script for data treatment, allowed for the successful confirmation of a single presence of TCs in the unknown samples. Overall, this work presents a straightforward study of the electrochemical behavior of TCs in SPE, allowing for the future on-site identification of residues of tetracycline antibiotics in real samples.

Advances and perspectives of aptasensors for the detection of tetracyclines: A class of model compounds of food analysis

The residual tetracyclines in food are frequently applied as the model compounds to develop aptasensors. Until now, more than 100 advanced aptasensors towards tetracyclines have been developed and published in English. This review summarizes and discusses comprehensively these advanced aptasensors, in terms of the principle designs, applied frontier transducers/materials, working performance, and advantages/disadvantages. The aptasensors are classified according to the inherent transduction techniques, i.e., optics, optics-electricity, optics-mass, and electricity-mass. Moreover, the present challenges such as the limited specificity and limited affinity of the aptamers, the future prospects and trends such as further combination with other advanced materials and technologies, and the urgent need of expanding the practical application were discussed and prospected. We hope this review can serve as a powerful tool for both tracing the development progresses of aptasensors and providing adequate references for further development of aptasensing methods for food-related analytes.

Near-infrared photoactive Yb-MOF functionalized with a large conjugate ionic liquid: synthesis and application for photoelectrochemical immunosensing of carcinoma embryonic antigen

A novel near-infrared (NIR)-excited photoelectrochemical (PEC) immunosensor based on an ionic liquid functionalized metal organic framework (Yb-MOF) and gold nanoparticles (Au-NPs) was designed for the high-performance determination of carcinoembryonic antigen (CEA). The Yb-MOF was synthesized from the coordination of the Yb3+ metal ion with the 1,1'-(1,5-dihydropyrene-2,7-diyl)bis(3-(4-carboxybenzyl)-1H-imidazol-3-ium) bromide [DDPDBCBIm(Br)2] ionic liquid by a hydrothermal method. To improve the photoelectric conversion efficiency of the Yb-MOF in the NIR region, the surface of the Yb-MOF was integrated with gold nanoparticles (AuNPs) to fabricate a Yb-MOF@AuNP nanocomposite through an in situ reduction of chloroauric acid with sodium borohydride. The NIR photoelectrochemical response of the Yb-MOF@AuNPs at 808 nm was enhanced 4-fold over the pristine Yb-MOF. Subsequently, a photoelectrochemical platform based on the Yb-MOF@AuNPs was constructed for loading the CEA antibody (anti-CEA). After cross-linking with glutaraldehyde followed by blocking with bovine serum albumin, a photoelectrochemical sensor for assaying CEA was fabricated. Upon specifically interacting with CEA, CEA can block the photogenerated electron-hole pair transfer and the mass transfer of ascorbic acid to the sensing interface, thus leading to a decrease in photocurrent response. The photocurrent variation can be used for determining CEA quantitatively. After optimizing the experimental conditions, the photocurrent variations before and after incubation with CEA were linearly correlated with the CEA concentration over the range of 0.005-15 ng mL-1. The detection limit of CEA was calculated to be 0.25 pg mL-1 (S/N = 3). The immunosensor was employed for the measurement of free CEA in clinical serum samples, and the results were very consistent with the values obtained by clinical tests. The NIR PEC immunosensor also demonstrated excellent accuracy and recovery, which corroborates its potential as a practical technique in clinical diagnosis.

A photoelectrochemical sensor based on Z-Scheme TiO2@Au@CdS and molecularly imprinted polymer for uric acid detection

A novel photoelectrochemical (PEC) sensor based on "Z-scheme" TiO₂@Au@CdS and molecularly imprinted polymer (MIP) was developed for the non-invasive detection of uric acid (UA). The "Z-scheme" material, consisting of an electron-transfer system (Au) and two isolated photochemical systems (CdS, TiO₂), was synthesized by chemical deposition method and it worked as a substrate for electro-polymerization of MIP. Due to the high photoelectric conversion efficiency provided by TiO₂@Au@CdS and specific imprinting effect afforded by MIP, the sensor displayed desirable sensing performance with the merits of sensitivity, selectivity, repeatability, and stability. The linear range for UA detection is from 1 nM to 9 μM with the detection limit of 0.3 nM (S/N = 3). Moreover, the assay was successfully utilized to measure UA in human tears and offered a reliable result. The incorporation of MIP and "Z-scheme" material into a PEC sensor system is expected to provide a promising strategy for detecting other small molecules.

Aptamer-Pendant DNA Tetrahedron Nanostructure Probe for Ultrasensitive Detection of Tetracycline by Coupling Target-Triggered Rolling Circle Amplification

Tetracycline (TET) is a broad-spectrum antibiotic, which is frequently used in the prevention and treatment of animal diseases, feed additives, and so on. However, its residue and accumulation in animal-derived foods could cause several side effects to the human body. Herein, we fabricated TET aptamer-pendant DNA tetrahedral nanostructure-functionalized magnetic beads (Apt-tet MBs) as a probe to detect TET. In the presence of target TET, DNA primer was released from Apt-tet MBs since the TET aptamer could specifically bind TET. Next, the separated DNA primer could effectively initiate rolling circle amplification (RCA) reaction and generate a long tandem single-stranded sequence. Finally, with SYBR Green I as the fluorescence dye, the fluorescence signal could be detected by detection probes through hybridizing the RCA product. Under optimal conditions, the fluorescent signal increased with the increasing target TET concentration within the 5 orders of magnitude dynamic range from 0.001 to 10 ng mL^-1. The detection limit was calculated to be 0.724 pg mL^-1 and the method showed high selectivity toward TET among different antibiotics. More impressively, this method was employed for TET determination in fish and honey samples. The as-obtained results were consistent with those of ELISA kits, holding great potential in the field of food analysis.

A dual-mode label-free electrochemical immunosensor for ultrasensitive detection of procalcitonin based on g-C3N4-NiCo2S4-CNTs-Ag NPs

Herein, a label-free electrochemical immunosensor based on differential pulse voltammetry (DPV) and amperometric i-t curve (i-t) dual-mode analysis is proposed for early quantitative detection of procalcitonin (PCT). Due to the advantages of high chemical stability and biocompatibility, graphite carbon nitride (g-C₃N₄) was adopted as a high-capacity sensing interface to carry signal indicators. As an effective indicator of chronoamperometry, nickel cobalt sulfide (NiCo₂S₄) was uniformly dispersed on the surface of g-C₃N₄ through in-situ hydrothermal synthesis, which not only promotes the activation of bimetallic activity, but also effectively prevents the aggregation of NiCo₂S₄. At the same time, in order to establish a dual-mode analysis platform to improve accuracy and sensitivity, highly conductive carbon nanotubes (CNTs) were hybridized with composite materials to load Ag nanoparticles (Ag NPs), which have excellent oxidizing properties and are used as indicators of DPV. On account of this advanced sensing strategy, a wide linear response (DPV: 0.05 ng mL^-1-50 ng mL^-1 and i-t: 1.00 pg mL^-1-10.00 ng mL^-1) and a low detection limit (DPV: 16.70 pg mL^-1 and i-t: 0.33 pg mL^-1) are demonstrated. The immunosensor synthesized by this method has good stability and sensitivity, which could be applied in clinical diagnosis and treatment.

Advances in Gold Nanoparticles-Based Colorimetric Aptasensors for the Detection of Antibiotics: An Overview of the Past Decade

Misuse of antibiotics has recently been considered a global issue because of its harmful effects on human health. Since conventional methods have numerous limitations, it is necessary to develop fast, simple, sensitive, and reproducible methods for the detection of antibiotics. Among numerous recently developed methods, aptasensors are fascinating because of their good specificity, sensitivity and selectivity. These kinds of biosensors combining aptamer with colorimetric applications of gold nanoparticles to recognize small molecules are becoming more popular owing to their advantageous features, for example, low cost, ease of use, on-site analysis ability using naked eye and no prerequisite for modern equipment. In this review, we have highlighted the recent advances and working principle of gold nanoparticles based colorimetric aptasensors as promising methods for antibiotics detection in different food and environmental samples (2011–2020). Furthermore, possible advantages and disadvantages have also been summarized for these methods. Finally, the recent challenges, outlook, and promising future perspectives for developing novel aptasensors are also considered.

Immunosorbent assay based on upconversion nanoparticles controllable assembly for simultaneous detection of three antibiotics

The abuse of antibiotics leads to an increase in resistant strains, which in turn leads to the development of superbugs that pose great difficulties for the treatment of human diseases. A high-throughput and highly sensitive avidin biotin complex immunosorbent assay based on upconversion nanoparticles controllable assembly (ABC-ULISA) for the detection of antibiotics was developed, which enabled accurate quantitative detection in a shorter period of time. Streptavidin and biotin-labeled upconversion nanoparticles form avidin-biotin-upconversion complex, which was then combined with biotinylated antibody to achieve double amplification of the signal, further improving detection sensitivity. Upconversion nanoparticles with 808 nm excitation provide better penetration without the need for an external source. The 96-well enzyme-linked plate was used as a detection platform to meet the high-throughput needs. ABC-ULISA was used to simultaneously detect three antibiotics with a limit of detection of 0.15 ng/mL for sulfamethazine, 0.03 ng/mL for sarafloxacin, and 0.05 ng/mL for tetracycline. The detection limit of ABC-ULISA was much lower than the traditional ELISA and ordinary ULISA. Moreover, ABC-ULISA was also versatile, and the corresponding target can be detected by changing different antibodies. The results were stable and reliable, and the equipment could be miniaturized, which was expected to be commercialized and on-site.

Photoelectrochemical thrombin biosensor based on perylene-3,4,9,10-tetracarboxylic acid and Au co-functionalized ZnO nanorods with signal-off quenching effect of Ag@Ag2S

In this work, a thrombin photoelectrochemical aptasensor was reported based on a photoanode of perylene-3,4,9,10-tetracarboxylic acid (PTCA), Au nanoparticle co-functionalized ZnO nanorods (ZnO NRs) and the "signal-off" amplification effect of Ag@Ag2S. The photocurrent response of the ZnO NRs was improved greatly due to the excellent visible-light photoelectric performance of PTCA and the surface plasmon resonance (SPR) effect of Au nanoparticles. Due to the specific recognition between thrombin and aptamers, the non-conductive complex with a steric hindrance structure blocked the diffusion path of the electron donating ascorbic acid (AA) and then the "signal-off" Ag@Ag2S quencher was captured. The quencher blocked the irradiation light toward the ZnO NRs/PTCA/Au electrode and competitively consumed the electron donor AA that could have been involved in the oxidation reaction with photogenerated holes of PTCA, resulting in the further decrease of the photocurrent. Based on the evident photocurrent response of the photoanode and the superior quenching strategies, the detection limit of thrombin is as low as 33 fM with a wide linear detection range from 0.0001 nM to 50 nM. The prepared biosensor also exhibited good specificity, reproducibility and stability, suggesting potential application in thrombin specific detection.

Preparation of PbS NPs/RGO/NiO nanosheet arrays heterostructure: Function-switchable self-powered photoelectrochemical biosensor for H2O2 and glucose monitoring

On the basis of synthesized PbS nanoparticles (PbS NPs)/reduced graphene oxide (RGO)/NiO nanosheet arrays (NiO NSAs) heterostructure, we constructed a function-switchable self-powered PEC sensing platform for the analysis of H2O2 and glucose. Ordered NiO NSAs have high electron mobility, modifying RGO onto the surfaces of NiO NSAs can connect the NiO NSAs with the PbS NPs and promoted the electron transfer rate between them, as well as enhance their photocurrent response. The PbS NPs/RGO/NiO NSAs heterostructure own excellent catalase-like activity can achieve H2O2 detection, only with one more step, after introducing glucose oxidase (GOD) onto the surface of PbS NPs/RGO/NiO NSAs heterostructure, we realized the detection conversion between H2O2 and glucose. Under optimal conditions, the proposed biosensor exhibited superior analytical performance toward H2O2 and glucose, a limit of detection (LOD) of 0.018 mM (S/N = 3) and 5.3 × 10-8 M (S/N = 3) were obtained, respectively. Moreover, good accuracy was obtained in the real samples analysis of H2O2 disinfectant and human serum samples.

A dual-response ratiometric fluorescent sensor by europium-doped CdTe quantum dots for visual and colorimetric detection of tetracycline

Residues in animal food and drinking water caused by the abuse of antibiotics lead to cell resistance and many chronic diseases in the human body. Therefore, it has become an inevitable trend to develop a fast, easy-to-use, on-site/real-time visualization method for the detection of antibiotics. Herein, we report a dual-response ratiometric fluorescence sensor which is fabricated by chelating europium ions (Eu³⁺) onto cadmium telluride quantum dots (CdTe QDs) for real-time and visible detection of tetracycline (TC). With the TC addition, the fluorescence of probe can be seen by the naked eye, from green to yellow and finally to red, exhibiting a dosage-sensitive and broad-chromatic detection strategy for TC. The fluorescence intensity ratio of I₆₁₆/I₅₁₂ of Eu/CdTe QDs sensor displays a good linear relation to TC concentrations in the range of 0-80 μM with a limit of detection (LOD) of 2.2 nM. In addition, the sensor can visually detect 200 nM TC in actual samples, which is lower than the maximum residue limit (MRL) of the safety standard. The methodology reported here opens a window toward the real applications of fluorescent and shows the wide applicability in pursuing the concepts simple, rapid, visual, and real-time for food safety and environmental protection.

Efficient BiVO4 photoanode decorated with Ti3C2TX MXene for enhanced photoelectrochemical sensing of Hg(II) ion

A highly sensitive photoelectrochemical (PEC) sensing platform was constructed for Hg²⁺ determination based on the Schottky heterojunction between an emerging 2D material Ti₃C₂T_X MXene and a promising semiconductor material BiVO₄. Through simply spin-coating the single-layer Ti₃C₂T_X onto the surface of BiVO₄ film, the modified electrode exhibited significantly enhanced PEC activity. However, the boost in photocurrent could be noticeably suppressed due to the consumption of hole-scavenging agents (reduced glutathione) by the added Hg²⁺. Owing to the selective decrease in the photocurrent with the addition of Hg²⁺, the PEC sensor based on BiVO₄/Ti₃C₂T_X displayed a wide linear range from 1 pM to 2 nM with the limit of detection down to 1 pM. Moreover, the PEC sensor also exhibited satisfactory accuracy and repeatability in practical sample water, the Yangtze River water, demonstrating the great potential for monitoring heavy metal ions in natural water resources.

Enhanced immobilization of mercury (II) from desulphurization wastewater by EDTA functionalized graphene oxide nanoparticles

Graphene oxide (GO) is a new promising nanometer material in a superconductor and wastewater heavy metal ions removal for its functionalized groups. Ethylenediaminetetraacetic acid functionalized graphene oxide complexes (EDTA-GO) was produced by a realizable silanization chemical reaction. Characteristics of Hg(II) removal in desulphurization wastewater was also under investigation. The chemical composition and microstructures of the EDTA-GO adsorbents were characterized by X-ray photoelectron spectroscopy (XPS), Transmission electron microscope (TEM), Scanning Electron Microscopy (SEM) analyses. To investigate the performance of EDTA-GO adsorbents on adsorption of Hg(II) in wastewater of wet flue gas desulphurization (WFGD), experiments were performed to optimize the main influence factors such as reaction temperatures (35-70°C), pH values(2-13), contact time (0-120 min), initial Hg(II) concentrations(800 ug/L) and adsorbent doses (20-50 mg/L). The maximum uptake removal efficiency (97.14%) was achieved under the optimal conditions at the pH of 7, the temperature of 70°C, the Hg(II) concentration of 1200 μg/L and the EDTA-GO dose of 40 mg/L. The kinetic data fitting results were well consistent with the pseudo-second-order model (R²= 0.99997) and a spontaneous and endothermic adsorption reaction was elaborated by thermodynamics studies (ΔG < 0, ΔH > 0, ΔS > 0). The experiments of recycled adsorbents by HCl generation were carried out to obtain the performance of the reused EDTA-GO adsorbent, the fourth regenerative adsorption efficiency still maintained 80.4%, which indicated that excellent potential application in desulphurization wastewater treatment.

A review: Recent advances in ultrasensitive and highly specific recognition aptasensors with various detection strategies

One of the most studied topics in analytical chemistry and physics is to develop bio-sensors. Aptamers are small single-stranded RNA or DNA oligonucleotides (5-25 kDa), which have advantages in comparison to their antibodies such as physicochemical stability and high binding specificity. They are able to integrate with proteins or small molecules, including intact viral particles, plant lectins, gene-regulation factor, growth factors, antibodies and enzymes. The aptamers have reportedly shown some unique characteristics, including long shelf-life, simple modification to provide covalent bonds to material surfaces, minor batch variation, cost-effectiveness and slight denaturation susceptibility. These features led important efforts toward the development of aptamer-based sensors, known as apta-sensors classified into optical, electrical and mass-sensitive based on the signal transduction mode. This review provided a number of current advancements in selecting, development criteria, and aptamers application with the focus on the effect of apta-sensors, specifically for disease-associated analyses. The review concentrated on the current reports of apta-sensors that are used for evaluating different food and environmental pollutants.

The versatile biomedical applications of bismuth-based nanoparticles and composites: therapeutic, diagnostic, biosensing, and regenerative properties

Studies of nanosized forms of bismuth (Bi)-containing materials have recently expanded from optical, chemical, electronic, and engineering fields towards biomedicine, as a result of their safety, cost-effective fabrication processes, large surface area, high stability, and high versatility in terms of shape, size, and porosity. Bi, as a nontoxic and inexpensive diamagnetic heavy metal, has been used for the fabrication of various nanoparticles (NPs) with unique structural, physicochemical, and compositional features to combine various properties, such as a favourably high X-ray attenuation coefficient and near-infrared (NIR) absorbance, excellent light-to-heat conversion efficiency, and a long circulation half-life. These features have rendered bismuth-containing nanoparticles (BiNPs) with desirable performance for combined cancer therapy, photothermal and radiation therapy (RT), multimodal imaging, theranostics, drug delivery, biosensing, and tissue engineering. Bismuth oxyhalides (BiO_x, where X is Cl, Br or I) and bismuth chalcogenides, including bismuth oxide, bismuth sulfide, bismuth selenide, and bismuth telluride, have been heavily investigated for therapeutic purposes. The pharmacokinetics of these BiNPs can be easily improved via the facile modification of their surfaces with biocompatible polymers and proteins, resulting in enhanced colloidal stability, extended blood circulation, and reduced toxicity. Desirable antibacterial effects, bone regeneration potential, and tumor growth suppression under NIR laser radiation are the main biomedical research areas involving BiNPs that have opened up a new paradigm for their future clinical translation. This review emphasizes the synthesis and state-of-the-art progress related to the biomedical applications of BiNPs with different structures, sizes, and compositions. Furthermore, a comprehensive discussion focusing on challenges and future opportunities is presented.

Detection signal amplification strategies at nanomaterial-based photoelectrochemical biosensors

This review focusses on unique material modification and signal amplification strategies reported in developing photoelectrochemical biosensors with utmost sensitivity and selectivity.

A photoelectrochemical aptasensor for the detection of 17β-estradiol based on In2S3 and CdS co-sensitized cerium doped TiO2

In₂S₃ and CdS co-sensitized Ce doped TiO₂ optimized the transmission path of electrons.

A new Bi2MoO6 nano-tremella-based electrochemical immunosensor for the sensitive detection of a carcinoembryonic antigen

Novel Bi₂MoO₆ nanohybrids with a tremella-like structure modified with gold nanoparticles were used to fabricate an electrochemical immunosensing platform of CEA.

Recent progress of heterostructure-based photoelectrodes in photoelectrochemical biosensing: a mini review

The heterostructure photoelectrodes have witted the rapid development to improve the performance of PEC biosensors recently.