Novel hybrid probe based on double recognition of aptamer-molecularly imprinted polymer grafted on upconversion nanoparticles for enrofloxacin sensing

Photocurrent switchable dual-target bioassay: Signal distinction and interface reconfiguration via pH-responsive triplex DNA programming

Most multiplexed photoelectrochemical (PEC) sensors require additional instrumentation and cumbersome electrode modification and surface partitioning, which limits their portability and instrument miniaturization. Herein, a pH-responsive programmable triple DNA nanomachine was developed for constructing a reconfigurable multiplex PEC sensing platform. By programming the base sequence, T-A·T-riched triple DNA was designed to construct integrated nano-controlled release machine (INCRM) for simultaneous recognition of multiple targets. The INCRM enables to recognize two targets in one step, and sequentially separate the signal labels by pH adjustment. The detached signal label catalyzes glucose to produce gluconic acid, causing the C-riched DNA fold into a triple structure on the electrode surface. As a result, one target can be detected relying on the enhanced photocurrent due to accelerated electron transfer between the CdS QD labeled at the end of C-riched DNA and the electrode. The triplex DNA dissociation in pH 7.4 buffer reconfigures the electrode interface, which can be continued to detect another target. The feasibility of the multiplexed sensor is verified by the detection of extensively coexisting antibiotics enrofloxacin (ENR) and ciprofloxacin (CIP). Under the optimal conditions, wide linear range (10 fg/mL ∼ 1 μg/mL) and low detection limit (3.27 fg/mL and 9.60 fg/mL) were obtained. The pH-regulated programmable triplex DNA nanomachine-based sensing platform overcomes the technical difficulties of conventional multiplexed PEC assay, which may open the way for miniaturization of multiplexed PEC sensors.

Engineering of dual recognition functional aptamer-molecularly imprinted polymeric solid-phase microextraction for detecting of 17β-estradiol in meat samples

In this study, an enhanced selective recognition strategy was employed to construct a novel solid-phase microextraction fiber coating for the detection of 17β-estradiol, characterized by the combination of aptamer biorecognition and molecularly imprinted polymer recognition. Benefiting from the combination of molecularly imprinted and aptamer, aptamer-molecularly imprinted (Apt-MIP) fiber coating had synergistic recognition effect. The effects of pH, ion concentration, extraction time, desorption time and desorption solvent on the adsorption capacity of Apt-MIP were investigated. The adsorption of 17β-estradiol on Apt-MIP followed pseudo-second order kinetic model, and the Freundlich isotherm. The process was exothermic and thermodynamically spontaneous. Compared with polymers that only rely on imprinted recognition, non-imprinted recognition or aptamer affinity, Apt-MIP had the best recognition performance, which was 1.30-2.20 times that of these three materials. Furthermore, the adsorption capacity of Apt-MIP for 17β-estradiol was 885.36-1487.52 times than that of polyacrylate and polydimethylsiloxane/divinylbenzone commercial fiber coatings. Apt-MIP fiber coating had good stability and could be reused for more than 15 times. Apt-MIP solid-phase microextraction coupled with high-performance liquid chromatography was successfully applied to the determination of 17β-estradiol in pork, chicken, fish and shrimp samples, with satisfactory recoveries of 79.61 %-105.70 % and low limits of detection (0.03 μg/kg). This work provides new perspectives and strategies for sample pretreatment techniques based on molecular imprinting technology and improves analytical performance.

Recent Advancements in Molecularly Imprinted Polymers Based Aptasensors: Critical Role of Nanomaterials for the Efficient Food Safety Analysis

Biosensors are being studied extensively for their ability to detect and analyze molecules. There has been a growing interest in combining molecular imprinted polymers (MIPs) and aptamers to create hybrid recognition elements that offer advantages such as target binding, sensitivity, selectivity, and stability. These hybrid elements have been successfully used in identifying a wide range of analytes in food samples. However, the application of MIP-based aptasensors in different sensing approaches is still challenging due to the low conductivity of MIPs-aptamers and limited adsorption capacity of MIPs. To address these limitations, researchers have been exploring the use of nanomaterials (NMs) to design efficient multiple-recognition systems that exploit the synergies between aptamers and MIPs. These hybrid systems can enhance the sensitivity and selectivity of MIP-based aptasensors in quantifying analytical samples. This review provides a comprehensive overview of recent advancements in the field of MIP-based aptasensors. It also introduces technologies that combine MIPs and aptamers to achieve higher sensitivity and selectivity in quantifying analytical samples. The review also highlights potential future trends and practical approaches that can be employed to address the limitations of MIP-based aptasensors, including the use of new NMs, the development of new fabrication techniques, and the integration of MIP-based aptasensors with other analytical tools.

Research progress on preparation methods and sensing applications of molecularly imprinted polymer-aptamer dual recognition elements

The aptamer (Apt) and the molecularly imprinted polymer (MIP), as effective substitutes for antibodies, have received widespread attention from researchers because of their creation. However, the low stability of Apt in harsh detection environment and the poor specificity of MIP have hindered their development. Therefore, some researchers have attempted to combine MIP with Apt to explore whether the effect of "1 + 1 > 2" can be achieved. Since its first report in 2013, MIP-Apt dual recognition elements have become a highly focused research direction in the fields of biology and chemistry. MIP-Apt dual recognition elements not only possess the high specificity of Apt and the high stability of MIP in harsh detection environment, but also have high sensitivity and affinity. They have been successfully applied in medical diagnosis, food safety, and environmental monitoring fields. This article provides a systematic overview of three preparation methods for MIP-Apt dual recognition elements and their application in eight different types of sensors. It also provides effective insights into the problems and development directions faced by MIP-Apt dual recognition elements.

A new and highly efficient CuMOF-based nanoenzyme and its application to the aptamer SERS/FL/RRS/Abs quadruple-mode analysis of ultratrace malachite green

Malachite green (MG) is highly toxic, persistent, and carcinogenic, and its widespread use is a danger to the ecosystem and a threat to public health and food safety, making it necessary to develop new sensitive multimode molecular spectroscopy methods. In this work, a new copper-based nanomaterial (CuNM) was prepared by a high-temperature roasting using a copper metal-organic framework (CuMOF) as precursor. The as-prepared CuNM was characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and BET surface area analysis. CuNM was found to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to produce the oxidation product TMBOX; however, subsequently, the MG aptamer (Apt) could be adsorbed on the CuNM surface by intermolecular interaction, which would inhibit the catalytic performance. After the addition of MG to be tested, the CuNM previously adsorbed by the Apt was transformed into its free state, thus restoring its catalytic activity. This new nanocatalytic indicator reaction could be monitored by surface-enhanced Raman scattering (SERS)/resonance Rayleigh scattering (RRS)/fluorescence (FL)/absorption (Abs) quadruple-mode methods. The SERS determination range was 0.004-0.4 nmol L-1 MG, with a limit of detection of 0.0032 nM. In this way, a rapid, stable, and sensitive method for the determination of MG residues in the environment was established.

Surface Functionalisation of Self-Assembled Quantum Dot Microlasers with a DNA Aptamer

The surface functionalisation of self-assembled colloidal quantum dot supraparticle lasers with a thrombin binding aptamer (TBA-15) has been demonstrated. The self-assembly of CdSSe/ZnS alloyed core/shell microsphere-shape CQD supraparticles emitting at 630 nm was carried out using an oil-in-water emulsion technique, yielding microspheres with an oleic acid surface and an average diameter of 7.3 ± 5.3 µm. Surface modification of the microspheres was achieved through a ligand exchange with mercaptopropionic acid and the subsequent attachment of TBA-15 using EDC/NHS coupling, confirmed by zeta potential and Fourier transform IR spectroscopy. Lasing functionality between 627 nm and 635 nm was retained post-functionalisation, with oleic acid- and TBA-coated microspheres exhibiting laser oscillation with thresholds as low as 4.10 ± 0.37 mJ·cm-2 and 7.23 ± 0.78 mJ·cm-2, respectively.

Characterization, specific recognition, and the performance in fish matrix of a shark-derived single-domain antibody against enrofloxacin

The third generation of genetic engineering antibodies, single-domain antibodies, have been widely reported as potential biomaterials in recognizing small molecular hazards. In this study, a shark-derived single-domain antibody was used as the recognition element for the first time to detect enrofloxacin (ENR), one of the most representative hazards in aquaculture. An ENR-specific clone named 2E6 was isolated by phage display technology. Experimental results proved that 2E6 ssdAb showed high affinity to ENR-PEI complete antigen, with the highest OD₄₅₀ value of 1.348 in binding ELISA. Through icELISA, it was determined that the IC₅₀ of 2E6 ssdAb to ENR was 19.230 ng/mL, while the IC₁₀ was 0.975 ng/mL, with rare recognition to other fluoroquinolones, which showed high sensitivity and specificity to ENR. The 2E6 ssdAb also performed excellently in fish matrix immunoassay. Results showed that the ENR-negative fish matrix did not seriously interfere with the recognition of 2E6 ssdAb to ENR-OVA, with the matrix index between 4.85% and 11.75%, while the results of icELISA in ENR-spiked fish matrix showed that 2E6 ssdAb could recognize the target ENR in different ENR-spiked concentrations of the fish matrix (10-1000 ng/mL), with the recovery between 89.30% and 126.38% and the RSD between 1.95% and 9.83%. This study broadens the application scenario of shark-derived single-domain antibodies as small molecule recognition biomaterials, providing a new recognition element on ENR detection for immunoassay.

Aptamer Sensors for the Detection of Antibiotic Residues- A Mini-Review

Food security is a global issue, since it is closely related to human health. Antibiotics play a significant role in animal husbandry owing to their desirable broad-spectrum antibacterial activity. However, irrational use of antibiotics has caused serious environmental pollution and food safety problems; thus, the on-site detection of antibiotics is in high demand in environmental analysis and food safety assessment. Aptamer-based sensors are simple to use, accurate, inexpensive, selective, and are suitable for detecting antibiotics for environmental and food safety analysis. This review summarizes the recent advances in aptamer-based electrochemical, fluorescent, and colorimetric sensors for antibiotics detection. The review focuses on the detection principles of different aptamer sensors and recent achievements in developing electrochemical, fluorescent, and colorimetric aptamer sensors. The advantages and disadvantages of different sensors, current challenges, and future trends of aptamer-based sensors are also discussed.

Electrochemical detection of enrofloxacin in meat using bimetallic organic framework-derived NiCo2O4@NiO

A novel electrochemical aptasensor based on a bimetallic organic frame-derived carbide nanostructure of Co and Ni (NiCo₂O₄@NiO) was prepared for rapid and sensitive enrofloxacin (ENR) detection of sheep and pork liver meats. The composite was fabricated by solvothermal and direct pyrolysis methods and dropped onto a modified electrode to improve the electron transfer efficiency. Furthermore, different techniques such as scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of the materials. Electrochemical impedance spectroscopy and cyclic voltammetry were used to evaluate the performance of the electrochemical sensor. As a result, the electrochemical aptasensor based on NiCo₂O₄@NiO exhibited excellent sensing performances for ENR with an extremely low detection limit of 1.67 × 10^-2 pg mL^-1 and a broad linear range of 5 × 10^-2 to 5 × 10⁴ pg mL^-1, as well as great selectivity, excellent reproducibility, high stability and applicability. In addition, the relative standard deviation for real samples was in the range of 93.83 to 100.09% and 94.95 to 100.01% for sheep and pork liver. The results showed that the composite can be expected to greatly facilitate ENR detection and practical applications in harmful food due to the advantages of simple fabrication, controllable, large-area uniformity, environmental friendliness, and trace detection.

MIPs-SERS Sensor Based on Ag NPs Film for Selective Detection of Enrofloxacin in Food

The quinolone antibiotics represented by enrofloxacin (ENRO) are harmful to the ecological environment and human health due to illegal excessive use, resulting in increasing food residues and ENRO levels in the environment. To this end, we developed a MIPs-SERS method using surface-enhanced Raman spectroscopy (SERS) and molecularly imprinted polymers (MIPs) to detect ENRO in food matrices. Firstly, a layer of silver nanoparticles (Ag NPs) with the best SERS effect was synthesized on the surface of copper rods as the enhancing material by in situ reductions, and then MIPs targeting ENRO were prepared by the native polymerization reaction, and the MIPs containing template molecules wrapped on the surface of silver nanoparticle films (Ag NPs-MIPs) were obtained. Our results showed that the Ag NPs-MIPs could specifically identify ENRO from the complex environment. The minimum detection limit for ENRO was 0.25 ng/mL, and the characteristic peak intensity of ENRO was linearly correlated to the concentration with a linear range of 0.001~0.1 μg/mL. The experimental results showed that in comparison to other detection methods, the rapid detection of ENRO in food matrices using Ag NPs-MIPs as the substrate is reliable and offers a cost-effective, time-saving, highly selective, and sensitive method for detecting ENRO residues in real food samples.

Reliable and Rapid Detection and Quantification of Enrofloxacin Using a Ratiometric SERS Aptasensor

Reliable detection and quantification of antibiotic residues in food using surface-enhanced Raman spectroscopy remain challenging, since the intensities of SERS signals are vulnerable to matrix and experimental factors. In this work, a ratiometric SERS aptasensor using 6-Carboxyl-X-Rhodamine (ROX)-labeled aptamers and 4-mercaptobenzonitrile (4-MBN)-functionalized gold nanoparticles (Au NPs) as SERS probes was established for the reliable and rapid detection and quantification of enrofloxacin. In the presence of enrofloxacin, the conformational transform of aptamers took place, and the distance between ROX and Au NP increased, which resulted in a decrease in the SERS signal intensity of ROX. Meanwhile, the intensity of the SERS signal of 4-MBN was used as an internal standard. Reliable determination of enrofloxacin was realized using the ratio of the SERS signal intensities of ROX to 4-MBN. Under optimal conditions, the developed ratiometric SERS aptasensor provided a wide linear range from 5 nM to 1 µM, with a correlation coefficient (R²) of 0.98 and a limit of detection (LOD) of 0.12 nM (0.043 ppb). In addition, the developed ratiometric SERS aptasensor was successfully applied for the determination of enrofloxacin in fish and chicken meat, with recovery values of 93.6-112.0%. Therefore, the established ratiometric SERS aptasensor is sensitive, reliable, time-efficient, and has the potential to be applied in the on-site detection of enrofloxacin in complex matrices.

A Comprehensive Review on Upconversion Nanomaterials-Based Fluorescent Sensor for Environment, Biology, Food and Medicine Applications

Near-infrared-excited upconversion nanoparticles (UCNPs) have multicolor emissions, a low auto-fluorescence background, a high chemical stability, and a long fluorescence lifetime. The fluorescent probes based on UCNPs have achieved great success in the analysis of different samples. Here, we presented the research results of UCNPs probes utilized in analytical applications including environment, biology, food and medicine in the last five years; we also introduced the design and construction of upconversion optical sensing platforms. Future trends and challenges of the UCNPs used in the analytical field have also been discussed with particular emphasis.

An advantageous application of molecularly imprinted polymers in food processing and quality control

In the global market era, food product control is very challenging. It is impossible to track and control all production and delivery chains not only for regular customers but also for the State Sanitary Inspections. Certified laboratories currently use accurate food safety and quality inspection methods. However, these methods are very laborious and costly. The present review highlights the need to develop fast, robust, and cost-effective analytical assays to determine food contamination. Application of the molecularly imprinted polymers (MIPs) as selective recognition units for chemosensors' fabrication was herein explored. MIPs enable fast and inexpensive electrochemical and optical transduction, significantly improving detectability, sensitivity, and selectivity. MIPs compromise durability of synthetic materials with a high affinity to target analytes and selectivity of molecular recognition. Imprinted molecular cavities, present in MIPs structure, are complementary to the target analyte molecules in terms of size, shape, and location of recognizing sites. They perfectly mimic natural molecular recognition. The present review article critically covers MIPs' applications in selective assays for a wide range of food products. Moreover, numerous potential applications of MIPs in the food industry, including sample pretreatment before analysis, removal of contaminants, or extraction of high-value ingredients, are discussed.

A novel terbium (III) and aptamer-based probe for label-free detection of three fluoroquinolones in honey and water samples

Fluoroquinolones, a family of synthetic broad-spectrum antibiotics, are widely used in clinical medicine, farm animals and aquaculture. Residues of fluoroquinolones in samples have attracted much attention because of growing food safety and public health concerns. Here, a novel Tb³⁺ ion-enrofloxacin aptamer coordination probe was prepared to develop a sensitive and rapid label-free fluorescence assay for specific detection three fluoroquinolones. In presence of the target, Tb³⁺ ion- enrofloxacin aptamer probe specifically bound with enrofloxacin, norfloxacin and ciprofloxacin, leading to a sharp increase in fluorescence emission of the probe. Under the optimized conditions, fluorescence increased linearly in the 1.0-100.0 ng/mL range for the three fluoroquinolones, with 0.053 ng/mL limit of detection for ciprofloxacin, 0.020 ng/mL limit of detection for norfloxacin and 0.061 ng/mL limit of detection for enrofloxacin. Satisfactory recovery (80.10-102.48%) in spiked honey and water samples were obtained for the three fluoroquinolones with relative standard deviations between 0.21% and 5.44% (n = 3).

Molecularly Imprinting–Aptamer Techniques and Their Applications in Molecular Recognition

Molecular imprinting–aptamer techniques exhibit the advantages of molecular imprinting and aptamer technology. Hybrids of molecularly imprinted polymer–aptamer (MIP–aptamer) prepared by this technique have higher stability, binding affinity and superior selectivity than conventional molecularly imprinted polymers or aptamers. In recent years, molecular imprinting–aptamer technologies have attracted considerable interest for the selective recognition of target molecules in complex sample matrices and have been used in molecular recognition such as antibiotics, proteins, viruses and pesticides. This review introduced the development of molecular imprinting–aptamer-combining technologies and summarized the mechanism of MIP–aptamer formation. Meanwhile, we discussed the challenges in preparing MIP–aptamer. Finally, we summarized the application of MIP–aptamer to the molecular recognition in disease diagnosis, environmental analysis, food safety and other fields.

Multivalent Aptamer Approach: Designs, Strategies, and Applications

Aptamers are short and single-stranded DNA or RNA molecules with highly programmable structures that give them the ability to interact specifically with a large variety of targets, including proteins, cells, and small molecules. Multivalent aptamers refer to molecular constructs that combine two or more identical or different types of aptamers. Multivalency increases the avidity of aptamers, a particularly advantageous feature that allows for significantly increased binding affinities in comparison with aptamer monomers. Another advantage of multivalency is increased aptamer stabilities that confer improved performances under physiological conditions for various applications in clinical settings. The current study aims to review the most recent developments in multivalent aptamer research. The review will first discuss structures of multivalent aptamers. This is followed by detailed discussions on design strategies of multivalent aptamer approaches. Finally, recent developments of the multivalent aptamer approach in biosensing and biomedical applications are highlighted.

Novel electrochemical sensor modified with molecularly imprinted polymers for determination of enrofloxacin in marine environment

Molecularly imprinted polymers were synthesized by gel-sol method with multi-walled carbon nanotubes as support and enrofloxacin as a template and further modified on the surface of glassy carbon electrode to construct a molecularly imprinted electrochemical sensor. The performance of the imprinted electrochemical sensor was thoroughly investigated by using cyclic voltammetry and differential pulse voltammetry. The influence of imprinted polymers amount, electrolyte pH, and incubation time on the sensor performance was investigated for the detection of enrofloxacin. Under the optimal experimental conditions in a three-electrode system with the modified electrode as the working electrode the differential pulse voltammetry response current of the sensor had a good linear relationship at 0.2 V (vs. saturated calomel reference electrode) with the enrofloxacin concentration within 2.8 pM-28 μM and the limit of detection of the method was 0.9 pM. The competitive interference experiment showed that the imprinted electrochemical sensor could selectively recognize enrofloxacin. The method was applied to analyze spiked natural seawater, fish, and shrimp samples. The recovery was 96.4%-102%, and RSD was less than 4.3% (n = 3), indicating that the proposed imprinted electrochemical sensor was suitable for the determination of trace enrofloxacin in marine environment samples.

Optical and Electrochemical Aptasensors for Sensitive Detection of Aflatoxin B1 and Aflatoxin M1 in Blood Serum, Grape Juice, and Milk Samples

Aflatoxin food contamination with toxic and carcinogenic impacts on human health is a global concern. We have developed aptasensors for the detection of Aflatoxin M₁ (AFM₁) and B₁ (AFB₁) using electrochemical and optical methods. In the first method, an electrochemical aptasensor was designed for the detection of AFM₁ based on complementary strand of AFM₁ aptamer that was attached onto the gold nanoparticles and a hairpin-shaped AFM₁ aptamer. The designed electrochemical aptasensor showed high selectivity toward AFM₁ with a limit of detection (LOD) as low as 0.9 nM. Moreover, the developed aptasensor was successfully used to detect AFM₁ in milk and serum with LODs of 1.8 and 1.2 nM, respectively. In the second method, a novel electrochemical aptasensor was developed based on the π-shape structure of AFB₁ aptamer. The detection limit was found to be 2 pg/mL in buffer. Also, the developed aptasensor was used to analyze AFB₁ spiked human serum and grape juice samples, and the recoveries were 95.4-108.1%. In another method, a fluorescent sensing scheme was developed for AFB₁ detection based on a hairpin structure of G-quadruplex oligonucleotide-aptamer chimera, streptavidin-coated silica nanoparticles (SNP-streptavidin) and N-methyl mesoporphyrin IX (NMM). The LOD was reported as 8 pg/mL with a linear range of 30-900 pg/mL. Moreover, the developed sensor could detect AFB₁ in serum and grape juice with the LOD of 9.8 and 11.2 pg/mL, respectively.

Molecular imprinted polymer combined with aptamer (MIP-aptamer) as a hybrid dual recognition element for bio(chemical) sensing applications. Review

The development of diagnostic devices based on memetic molecular recognitions are becoming highly promising due to high specificity, sensitivity, stability, and low-cost comparing to natural molecular recognition. During the last decade, molecular imprinted polymers (MIPs) and aptamer have shown dramatic enhancement in the molecular recognition characteristics for bio(chemical) sensing applications. Recently, MIP-aptamer, as an emerging hybrid recognition element, merged the advantages of the both recognition components. This dual recognition-based sensor has shown improved properties and desirable features, such as high sensitivity, low limit of detection, high stability under harsh environmental conditions, high binding affinity, and superior selectivity. Hybrid MIP-aptamer as dual recognition element, was used in the real sample analysis, such as detection of proteins, neurotransmitters, environmental pollutants, biogenic compounds, small ions, explosives, virus detections and pharmaceuticals. This review focuses on a comprehensive overview of the preparation strategies of various MIP-aptamer recognition elements, mechanism of formation of MIP-aptamer, and detection of various target molecules in different matrices.

Ultrasensitive near-infrared aptasensor for enrofloxacin detection based on wavelength tunable AgBr nanocrystals electrochemiluminescence emission triggered by O-terminated Ti3C2 MXene

Toxic-free and easily accessible electrochemiluminescence (ECL) emitter/luminophore with near-infrared (NIR) emission is highly anticipated for ECL biosensor evolution. In this study, well-dispersed AgBr nanocrystals (NCs) decorated Ti₃C₂ MXene nanocomposites (Ti₃C₂-AgBrNCs) were prepared using a simple wet chemical technique and demonstrated highly efficient NIR ECL emission. For the first time, Ti₃C₂-AgBrNCs displayed wavelength-tunable ECL emission with varied Ti₃C₂ contents. Interestingly, further experimental data revealed that the ECL emission wavelength of Ti₃C₂-AgBrNCs red-shifted from 550 to 665 nm as Ti₃C₂ content increased, which can be attributed to the surface-defect effect generated by the oxygen-containing functional groups in Ti₃C₂ MXene. In particular, the ECL emission at 665 nm of Ti₃C₂-AgBrNCs nanocomposites not only revealed a 3.5 times increased ECL intensity but also a more stable ECL signal compared to pure AgBr NCs. As a proof of concept, a direct-type NIR ECL aptasensor with signal-on strategy was constructed with the Ti₃C₂-AgBrNCs nanocomposites as an ECL platform and enrofloxacin (ENR) as a model analyte. The NIR ECL aptasensor exhibited high sensitivity, a wide linear range from 1.0 × 10^-12 mol/L to 1.0 × 10^-6 mol/L and a low detection limit (5.97 × 10^-13 mol/L). This research offered a viable alternative way for producing toxic-free and efficient near-infrared ECL luminophores in bioanalysis and wavelength-tuning light-emitting devices.

A sensitive aptasensor based on rolling circle amplification and G-rich ssDNA/terbium (III) luminescence enhancement for ofloxacin detection in food

As the light-harvesting "antenna", G-rich oligonucleotides (such as the G-quadruplex) can interact with lanthanide (III) to bring a luminescent enhancement response. In this study, phenomenon of luminescent enhancement of G-triplex/terbium (III) (G3/Tb³⁺) and interaction between G3 and Tb³⁺ were first reported and characterized. Based on G3/Tb³⁺ luminescence, a label-free aptasensor for the detection of ofloxacin (OFL) residues in the food was developed. The OFL triggered the action of rolling circle amplification (RCA) allowed for the amplification product of G3-forming sequences in the single-stranded DNA, which promoted the conformational transition of the G3/Tb³⁺ complexes once the addition of Tb³⁺. Under the optimal conditions, the logarithmic correlation between the G3/Tb³⁺ luminescence intensity and the concentration of OFL was found to be linear in the range of 5-1000 pmol L^-1 (R² = 0.9949). The limit of detection was 0.18 pmol L^-1 (3σ/slope). Additionally, the good recoveries of 90.19-108.89 % and the relative standard deviations values of 0.59-5.87 % were obtained in the application of the aptasensor detecting OFL in the practical samples. These results confirmed that the present aptasensor has a good analytical performance and bright prospect for detecting ofloxacin residues in food.

Conjugated bimetallic cobalt/iron polyphthalocyanine as an electrochemical aptasensing platform for impedimetric determination of enrofloxacin in diverse environments

The synthesis of bimetallic cobalt/iron polyphthalocyanine (represented by polyCoFePc) network via a modified solid-phase synthesis method is described. It was exploited as a platform for anchoring enrofloxacin (ENR)-targeted aptamer strands, thus, fabricating a label-free impedimetric aptasensor for determination of ENR. The polyCoFePc exhibited a porous two-dimensional (2D) conjugated nanostructure and rich functional groups, and showed a superior binding interaction toward aptamer strands as compared to monometallic polyFePc and polyCoPc networks. This finding was attributed to structural defects and increased active binding sites, thereby giving a highly sensitive detection ability toward ENR. By using electrochemical impedance spectroscopy (EIS), the polyCoFePc-based electrochemical aptasensor exhibited an extremely low detection limit of 0.06 fg mL^-1 within the ENR concentration from 0.1 fg mL^-1 to 100 pg mL^-1, along with high selectivity, good reproducibility, and remarkable stability. Interestingly, the constructed polyCoFePc-based aptasensor also demonstrated wide practicability in various environments. The recoveries of ENR spiked into river water, milk, and pork samples ranged within 91.2 - 107.2%, 90.5 - 109.6%, and 91.2 - 102.3%, respectively.

Research and Application of Highly Selective Molecular Imprinting Technology in Chiral Separation Analysis

Since residual chiral pollutants in the environment and toxic or ineffective chiral components in drugs can threat human health, there is an urgent need for methods to separation and analyze chiral molecules. Molecular imprinting technology (MIT) is a biomimetic technique for specific recognition of analytes with high potential for application in the field of chiral separation and analysis. However, since MIT has some disadvantages when used for chiral recognition, such as poor rigidity of imprinted materials, a single type of recognition site, and poor stereoselectivity, reducing the interference of conformationally and structurally similar substances to increase the efficiency of chiral recognition is difficult. Therefore, improving the rigidity of imprinted materials, increasing the types of imprinted cavity recognition sites, and constructing an imprinted microenvironment for highly selective chiral recognition are necessary for the accurate identification of chiral substances. In this article, the principle of chiral imprinting recognition is introduced, and various strategies that improve the selectivity of chiral imprinting, using derivative functional monomers, supramolecular compounds, chiral assembly materials, and biomolecules, are reviewed in the past 10 years.

Functional Hybrid Micro/Nanoentities Promote Agro-Food Safety Inspection

The rapid development of nanomaterials has provided a good theoretical basis and technical support to solve the problems of food safety inspection. The combination of functionalized composite nanomaterials and well-known detection methods is gradually applied to detect hazardous substances, such as chemical residues and toxins, in agricultural food products. This review concentrates on the latest agro-food safety inspection techniques and methodologies constructed with the assistance of new hybrid micro/nanoentities, such as molecular imprinting polymers integrated with quantum dots (MIPs@QDs), molecular imprinting polymers integrated with upconversion luminescent nanoparticles (MIPs@UCNPs), upconversion luminescent nanoparticles combined with metal-organic frameworks (UCNPs@MOFs), magnetic metal-organic frameworks (MOFs@Fe₃O₄), magnetic covalent-organic frameworks (Fe₃O₄@COFs), covalent-organic frameworks doped with quantum dots (COFs@QDs), nanobody-involved immunoassay for fast inspection, etc. The presented summary and discussion favor a relevant outlook for further integrating various disciplines, like material science, nanotechnology, and analytical methodology, for addressing new challenges that emerge in agro-food research fields.

Lanthanide upconversion and downshifting luminescence for biomolecules detection

Biomolecules play critical roles in biological activities and are closely related to various disease conditions. The reliable, selective and sensitive detection of biomolecules holds much promise for specific and rapid biosensing. In recent years, luminescent lanthanide probes have been widely used for monitoring the activity of biomolecules owing to their long luminescence lifetimes and line-like emission which allow time-resolved and ratiometric analyses. In this review article, we concentrate on recent advances in the detection of biomolecule activities based on lanthanide luminescent systems, including upconversion luminescent nanoparticles, lanthanide-metal organic frameworks, and lanthanide organic complexes. We also introduce the latest remarkable accomplishments of lanthanide probes in the design principles and sensing mechanisms, as well as the forthcoming challenges and perspectives for practical achievements.

Exploring the use of upconversion nanoparticles in chemical and biological sensors: from surface modifications to point-of-care devices

Upconversion nanoparticles (UCNPs) have emerged as promising luminescent nanomaterials due to their unique features that allow the overcoming of several problems associated with conventional fluorescent probes. Although UCNPs have been used in a broad range of applications, it is probably in the field of sensing where they best evidence their potential. UCNP-based sensors have been designed with high sensitivity and selectivity, for detection and quantification of multiple analytes ranging from metal ions to biomolecules. In this review, we deeply explore the use of UCNPs in sensing systems emphasizing the most relevant and recent studies on the topic and explaining how these platforms are constructed. Before diving into UCNP-based sensing platforms it is important to understand the unique characteristics of these nanoparticles, why they are attracting so much attention, and the most significant interactions occurring between UCNPs and additional probes. These points are covered over the first two sections of the article and then we explore the types of fluorescent responses, the possible analytes, and the UCNPs' integration with various material types such as gold nanostructures, quantum dots and dyes. All the topics are supported by analysis of recently reported sensors, focusing on how they are built, the materials' interactions, the involved synthesis and functionalization mechanisms, and the conjugation strategies. Finally, we explore the use of UCNPs in paper-based sensors and how these platforms are paving the way for the development of new point-of-care devices.

Dual-recognition colorimetric sensing of thrombin based on surface-imprinted aptamer-Fe3O4

Thrombin plays an essential role in blood coagulation and some physiological and pathological processes. The convenient, rapid, sensitive, and specific detection of thrombin is of great significance in clinical research and diagnosis. Herein, surface molecularly imprinted polymer (MIP) was modified on aptamer-functionalized Fe3O4 nanoparticles (MIP-aptamer-Fe3O4 NP) for thrombin colorimetric assay by taking advantage of the peroxidase-like activity of Fe3O4 NP. With the adsorption of thrombin into imprinted cavities, the exposed surface area of Fe3O4 NP decreased, causing a decrease in its peroxidase-like activity toward 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. On the other hand, the reductive amino acids on the thrombin surface also impeded the oxidation of TMB. Both phenomena caused the light blue color of the sensing solution. Thus, a specifically sensitive colorimetric approach for the visual detection of thrombin was proposed with a linear range and limit of detection of 108.1 pmol L-1-2.7 × 10-5 mol L-1 and 27.8 pmol L-1, respectively. Moreover, due to the double recognition elements of MIP and aptamer, the prepared MIP-aptamer-Fe3O4 NP showed higher selectivity to thrombin than that based on only one recognition element. It is worth noting that no special property (e.g. electrochemical or fluorescence activity) of the template was required in this work. Thus, more template molecules can be easily, selectively, and sensitively detected based on the proposed MIP-aptamer-mimic enzyme colorimetric sensing strategy.

Simultaneous detection of enrofloxacin and ciprofloxacin in milk using a bias potentials controlling-based photoelectrochemical aptasensor

It is important to develop highly-active photoelectrochemical (PEC) materials and use novel sensing strategy for constructing high-PEC-performance sensors with multiplex detection abilities, owing to the simultaneous presence of multiple antibiotic residues in food. Herein, a bias-potential-based PEC aptasensor was prepared for the trace detection of dual antibiotic analytes, enrofloxacin (ENR) and ciprofloxacin (CIP), which often coexist in milk samples. Here, two materials were developed with excellent PEC performance: three-dimensional nitrogen-doped graphene-loaded copper indium disulfide (CuInS₂/3DNG) and Bi³⁺-doped black anatase titania nanoparticles decorated with reduced graphene oxide (Bi³⁺/B-TiO₂/rGO). By applying different bias potentials to the two materials near one ITO electrode, the cathodic current generated by CuInS₂/3DNH and the anodic current generated by Bi³⁺/B-TiO₂/rGO could be clearly distinguished without interfering with each other. Then, ENR and CIP aptamers were respectively modified onto the surface of CuInS₂/3DNH and Bi³⁺/B-TiO₂/rGO to construct a PEC aptasensor for the sensitive detection of ENR and CIP. Under optimal conditions, the proposed aptasensor exhibited wide linear ranges of ENR (0.01-10000 ng/mL) and CIP (0.01-1000 ng/mL), and relatively low detection limits of 3.3 pg/mL to ENR and CIP (S/N = 3). The aptasensor was successfully applied to the detection of ENR and CIP in milk samples.

Recent advances in biosensors for antibiotic detection: Selectivity and signal amplification with nanomaterials

Antibiotics are widely used in the prevention and treatment of infectious diseases in animals due to its bactericidal or bacteriostatic action. Residual antibiotics and their metabolites pose great threats to human and animal health, such as potential carcinogenic and mutagenic effects, and bacterial resistances. Therefore, it is necessary and urgent to accurately monitor trace amounts of antibiotics in food samples. Up to now, many analytical methods have been reported for the determination of antibiotics. Biosensors with the advantages of high sensitivity, rapid response, easy miniaturization, and low price have been widely applied to the detection of antibiotics residues in past decades. This review offered an in-depth evaluation of recognition elements for antibiotic residues in diverse food matrices. In addition, it presented a systematical and critical review on signal amplification via various materials, focusing on recently developed nanomaterials. Finally, the review provided an outlook on the future concepts to help upgrade the sensing techniques for antibiotics in food.

Novel impedimetric sensing strategy for detecting ochratoxin A based on NH2-MIL-101(Fe) metal-organic framework doped with cobalt phthalocyanine nanoparticles

Iron-based metal-organic framework, NH₂-MIL-101(Fe), was doped with different dosages of cobalt phthalocyanine nanoparticles (CoPc) to synthesize a series of NH₂-MIL-101(Fe)@CoPc nanocomposites. The NH₂-MIL-101(Fe)@CoPc nanocomposites were then employed to construct novel impedimetric aptasensors for the detection of ochratoxin A (OTA). Combining the intrinsic advantages of NH₂-MIL-101(Fe) (highly porous structure and excellently electrochemical activity) and CoPc (good physiochemical stability and strong bioaffinity), the NH₂-MIL-101(Fe)@CoPc nanocomposites show promising properties, which are beneficial for immobilizing OTA-targeted aptamer strands. Amongst, the developed impedimetric aptasensor based on NH₂-MIL-101(Fe)@CoPc_6:1, prepared using the mass ratio of NH₂-MIL-101(Fe):CoPc of 6:1, exhibits the best amplified electrochemical signal and highest sensitivity for detecting OTA. The detection limitation is 0.063 fg·mL^-1 within the OTA concentration of 0.0001-100 pg·mL^-1, accompanying with high selectivity, good reproducibility and stability, acceptable regenerability, and wide applicability in diverse real samples. Consequently, the proposed sensing strategy can be applied for detecting OTA to cope with food safety.

Hybrid aptamer-molecularly imprinted polymer (AptaMIP) nanoparticles selective for the antibiotic moxifloxacin

A polymerisable aptamer incorporated into Molecularly Imprinted Polymer nanoparticles (MIPs) creates a hybrid “best-of-both-worlds” approach which outperforms individual constituent components.

Fabrication of an electrochemical biodevice for ractopamine detection under a strategy of a double recognition of the aptamer/molecular imprinting polymer

The importance of RAC tracking in human biofluids has boosted many demands for designing an ultrasensitive tool to determine the trace value of the RAC from clinical, judicial, and forensic centers. In this study, an electrochemical biodevice has developed for the highly selective detection of this illegal feed additive under a double recognition strategy of the aptamer (Apt) and molecular imprinting polymer (MIP) on a glassy carbon electrode (GCE). The sensing relies on this fact that both the MIP and Apt act synergistically to trap the RAC molecules. The sensing surface fabrication steps have been monitored by some electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV(. The charge transfer resistance (R_ct) value of the redox probe as a representative of the biodevice response has increased linearly with the RAC concentration increasing in a dynamic range of 1 fM to 1.90 µM. The detection limit (LOD) value has been estimated to be 330 aM, lower than all of the reported methods in the RAC sensing. Furthermore, the practical feasibility of biodevice has been evaluated in some human blood serum and urine samples. This strategy offers some useful advantages in reliable detection of the RAC, which may help in the routine analysis, as mandated by regulatory agencies.

Sensors/nanosensors based on upconversion materials for the determination of pharmaceuticals and biomolecules: An overview

Upconversion materials have been the focus of a large body of research in analytical and clinical fields in the last two decades owing to their ability to convert light between various spectral regions and their particular photophysical features. They emit efficient and sharp ultraviolet (UV) or visible luminescence after excitation with near-infrared (NIR) light. These features overcome some of the disadvantages reported for conventional fluorescent materials and provide opportunities for high sensitivity chemo-and bio-sensing. Here, we review studies that used upconversion materials as sensors for the determination of pharmaceuticals and biomolecules in the last two decades. The articles included in this review were retrieved from the SCOPUS database using the search phrases: "upconversion nanoparticles for determination of pharmaceutical compounds", and "upconversion nanoparticles for determination of biomolecules". Details of each developed upconversion nanoparticles based sensor along with their relevant analytical parameters are reported and carefully explained.

Interaction of LiYF4:Yb3+/Er3+/Ho3+/Tm3+@LiYF4:Yb3+ upconversion nanoparticles, molecularly imprinted polymers, and templates

In this work, LiYF₄:Yb_0.25³⁺/Er_0.01³⁺/Tm_0.01³⁺/Ho_0.01³⁺@LiYF₄:Yb_0.2³⁺ upconverting nanoparticles (UCNP) were used as luminescent materials for the preparation of molecular imprinting polymer nanocomposites. Three luminescent molecularly imprinted polymer (MIP) nanocomposites were prepared by in situ polymerization. The relationship between the functional monomers, templates, and upconversion nanoparticles was investigated. Two hydrophilic monomers (acrylic acid (AA) and acrylamide (AAm)) and one hydrophobic monomer (N-tert-butylacrylamide (TBAm)) were employed as functional monomers, while one amino acid (cysteine) and two proteins (albumin and hemoglobin) were employed as the templates to investigate the effect of their interaction with LiYF₄:Yb³⁺/Er³⁺/Ho³⁺/Tm³⁺@LiYF₄:Yb³⁺ core/shell UCNPs on the polymerization process, luminescence properties, and adsorption capacity. The results showed that the UCNPs were embedded in the polymeric matrix to form an irregular quasimicrospherical UCNPs@MIP with diameters ranging from several hundred nanometers to several micrometers depending on the functional monomer. The quenching effect was more pronounced for the adsorption of hemoglobin with UCNPs@MIP compared to cysteine and albumin. In addition, the adsorption capacities of the AA- and AAm-made UCNPs@MIP were greater than those of TBAm-made UCNPs@MIP. The rebinding of the templates onto UCNPs@MIP was very fast and approached equilibrium within 30 min, indicating that the synthesized UCNPs@MIP can be employed as fluorescent probes to offer rapid detection of molecules.

In this work, LiYF₄:Yb_0.25³⁺/Er_0.01³⁺/Tm_0.01³⁺/Ho_0.01³⁺@LiYF₄:Yb_0.2³⁺ upconverting nanoparticles (UCNP) were used as luminescent materials for the preparation of molecular imprinting polymer nanocomposites.

A rational route to hybrid aptamer-molecularly imprinted magnetic nanoprobe for recognition of protein biomarkers in human serum

Although antibody has played a great role in highly specific recognition of protein biomarkers, it faces poor stability, reproducibility, high-cost and time-consuming preparation, etc. Here, aptamer and molecularly imprinted polymers (MIPs), both as promising substitutes of antibody, were integrated onto magnetic nanoparticles by Au-S bonds and SiO₂ as imprinted layer for preparing a new nanoprobe. Highly specific and sensitive recognition of different protein biomarkers, such as insulin for diabetes and alpha-fetoprotein (AFP) for hepatic carcinoma, were achieved respectively by the system of combining hybrid aptamer-molecularly imprinted magnetic nanoprobe and mass spectrometry. With the double affinities offered by aptamer-MIPs, insulin can be detected at 0.5 ng mL^-1 in human serum dilution, the equlibrium dissociation constant between nanoprobe and insulin is measured as 23.61 ± 2.27 μM. Likewise, AFP can be sufficiently detected in human saliva dilution from 1000 ng mL^-1 to 20 ng mL^-1, and two patients with hepatic carcinoma are discriminated from healthy person due to the abnormally high expression of AFP in serum.

Terminal-conjugated non-aggregated constraints of gold nanoparticles on lateral flow strips for mobile phone readouts of enrofloxacin

Antibiotics abuse now poses a global threat to public health. Monitoring their residual levels as well as metabolites are of great importance, still challenges remain in in situ tracing during the circulation. Herein, taking the typical antibacterial Enrofloxacin (ENR) as a subject, a paper-based aptasensor was tailored by manipulating a duo of aptameric moieties to "sandwich" the target in a lateral-flow regime. To visualize the tight-binding sandwich motif more vividly, an irregular yet robust DNA-bridged gold nanoparticles (AuNPs) proximity strategy was developed with recourse to terminal deoxynucleotidyl transferase, of which the nonaggregate constraining feature was unveiled via optical absorption and scanning probe topography. This complex performed exceptionally better in the test strip context than single-particle tags, leading to an enhanced on-chip focusing. Rather than qualitative color developing, further efforts were taken to visualize the readouts in a quantitative manner by exploiting the smartphone camera for pattern recognition along with data processing in a professional App. Overall, this prototyped contraption realized a rapid and ultrasensitive quantification of ENR down to 0.1 μg/L along with a broad linear range over 5 orders of magnitude, plus excellent selectivity and precision even for real samples. Such innovative fusion across DNA-structured nanomanufacturing and intelligent perception provides a prospective and invigorating solution to point-of-care inspection.