A label-free colorimetric aptasensor based on controllable aggregation of AuNPs for the detection of multiplex antibiotics

Enhanced quenching efficiency of UiO-66-NH2 over UiO-66 to engineer high-performance fluorescence aptasensor for oxytetracycline monitoring

Oxytetracycline (OTC), a broad class of antibacterial medication, has been widely utilized in poultry husbandry and fish farming. However, the presence of OTC residues in the food has become a matter of great concern. These residues have the potential to induce the emergence and spread of bacterial resistance, which can have far-reaching consequences for public health. In this work, we focused on the comparison of the quenching efficiency of UiO-66 and its amino group-modified counterpart UiO-66-NH2, towards the fluorescence of nitrogen-doped graphene quantum dots (NGQDs) labeled aptamer (NGQDs-apt). It was found that UiO-66-NH2 demonstrated a more potent fluorescence quenching ability towards NGQDs-apt, as high as 98.8 %, compared to 69.7 % for UiO-66 without amino functionalization. This enhanced performance is attributed to the improved interaction between the amino groups on UiO-66-NH2 and the NGQDs-apt, facilitating more effective electron transfer. Consequently, UiO-66-NH2 was selected as the optimal quencher for the development of a highly sensitive aptasensor. This aptasensor demonstrates a quantitative detection range for OTC spanning from 0.001 to 200 μM with an exceptionally low detection limit of 0.25 nM, showing simplicity, accuracy, stability and great potential for antibiotic residue detection in food samples. This work addresses the urgent need to develop reliable methods for detecting OTC residues in food due to the potential of OTC to trigger bacterial resistance, which is crucial for food safety and public health.

Graphene FET biochip on PCB reinforced by machine learning for ultrasensitive parallel detection of multiple antibiotics in water

Antibiotics like Ciprofloxacin (Cfx), tetracycline (Tet) and Tobramycin (Tob) are commonly used against a broad-spectrum of bacterial infection. Recent surge in their uptake through the presence of their residues in environmental water has been linked to increased antibiotic resistance. Conventional methods for antibiotic monitoring by gold standards like LC-MS though sensitive and reliable, are expensive, requires dedicated equipment and complex sample processing steps. In this context, nanoscale field-effect transistors (FETs) present significant advantages of rapid measurement and ultra-high sensitivity but the device-device variations in the transfer characteristics originating from the inherent fluctuations in fabrication protocol of 2D materials, lead to stochasticity in bioreceptor orientation and binding densities which limits their potential for ultrasensitive and reliable detection of multiple antibiotics in river water. Here, we introduce a distinctive approach for few femtomolar detection of Cfx, Tet and Tob simultaneously in river water by developing thermally reduced graphene oxide (TRGO) FET array on printed circuit board utilizing copper plated electrodes where multiple features extracted from sensor transfer characteristics are processed by machine learning models, trained with moderate calibration dataset. The demonstrated methodology detects 1 fM concentration of Cfx, Tet and Tob with satisfactory accuracy within 20 min, using XGBoost model. The achieved detection limit is three and two orders of magnitude lower than previous reports of multiple and single antibiotic detection respectively. The TRGO FET sensor array interfaced with an electronic readout imparts capability to track the concentration of antibiotic contaminants in various water sources and adopt necessary measures for safe drinking water.

Multi-group structure analysis and molecular docking of aptamers and small molecules: A case study of chloramphenicol

Aptamers, a kind of short nucleotide sequences with high specificity and affinity with targets, have attracted extensive attention in recent years. Molecular docking method (MDM) is the most common method to explore the binding mode and recognition mechanism of aptamers and small molecules, which generally use the target to dock with the highest scoring tertiary structural model of the aptamer, and the highest scoring result is used as the predicted model. However, this prediction results may miss out the true interaction pattern due to the fact that aptamers are not completely rigid and the natural aptamers conformations are not in a single state. Thus, evaluation of the binding pattern from two or more tertiary structural modes might be more accurate. The use of chloramphenicol (CAP) has been banned because it causes myelosuppression and aplastic anemia in humans. However, CAP is still abused and is often studied as a target for detection. Two CAP aptamers (Apt-11 and Apt-16) were used as cases in this study. All secondary structures of these two aptamers were predicted using the UNAFold Web Server tool, and then the corresponding tertiary structure models were built using the RNA Composer tool and Discovery Studio 4.5 Client software. The resulted six tertiary structure models were docked with CAP respectively. By optimizing the docking conditions, multiple groups of docking outcomes were obtained, including the tertiary structure, its binding free energy, and the binding site. The results suggested that there may be multiple binding sites in the same tertiary structure, and the binding energy of the same tertiary structure as well as the proportion of multiple binding sites vary greatly. In addition, it was found that Autodock4 works well in analyzing the binding mode between screened aptamers with its defined target, but cannot be used to identify that whether an aptamer could bind well with other molecule with big structural difference from the target. The CAP aptamer was tailored according to the molecular docking results, and the potential binding sites with CAP were verified by a colloidal gold colorimetry assay. In conclusion, we propose a method to explore the binding patterns between aptamer and its targets by using multiple optimized docking data from different tertiary structures of the aptamer, which provides a theoretical basis for the study of the binding mode of aptamers and targets, as well as the optimization and modification of aptamers.

Antiprotein Corona-Fouling Effect of the Double-Stranded DNA Coating Layer on the Gold Nanoparticles-Small Molecule Adsorbent Probe

The formation of a protein corona (PC) can significantly impact the detection ability of gold nanoparticles (AuNPs)-small molecule adsorbent probes based on competitive adsorption. To alleviate this problem, in this study, double-stranded DNA (dsDNA) was introduced to modify the AuNP probes to mitigate the negative effect of PCs on the detection of small molecules by taking the AuNPs-dichlorofluorescein (DCF) probe-based detection of ambroxol hydrochloride (AMB) as a study model. It was found that based on the dsDNA-modified AuNPs-DCF probe (dsDNA@AuNPs-DCF), the accuracy for the detection of AMB was significantly improved, which might be attributed to the isolation of proteins from the surface of AuNPs while still allowing small molecules to access the surface due to the introduction of rigid dsDNA. Further, the effect of the strand length and the number of dsDNA modified on the surface of AuNPs on the antifouling performance was then investigated, and it was found that the LOD value of AMB in artificial milk samples by dsDNA10bp90@AuNPs-DCF probes (with 10 base strand length and 90:1 ratio of dsDNA to AuNPs) is decreased more than 2-fold compared with that by the AuNPs-DCF probe. Moreover, based on dsDNA10bp90@AuNPs-DCF probes, the recovery rates of AMB analyzed in commercial milk samples greatly improved compared with that with the AuNPs-DCF probe, particularly when the samples contained AMB with much lower concentrations. This study demonstrates a dsDNA-based antiprotein corona-fouling strategy for the AuNPs-small molecule adsorbent probe, which provides beneficial ideas for dealing with the interference resulting from PCs to the studying of biological samples.

A Label-Free Aptasensor for the Detection of Sulfaquinoxaline Using AuNPs and Aptamer in Water Environment

Sulfaquinoxaline (SQX) is widely utilized in aquaculture and animal husbandry due to its broad antimicrobial spectrum and low cost. However, it is difficult to degrade, and there are relevant residues in the aquatic environment, which could be harmful to both the ecological environment and human health. As a new recognition molecule, the aptamer can be recognized with SQX with high affinity and specificity, and the aptamer is no longer adsorbed to AuNPs after binding to SQX, which weakens the catalytic effect of AuNPs. Consequently, an aptasensor for the detection of SQX was successfully developed. This aptasensor exhibits a linear range of 40-640 ng/mL, with a detection limit of 36.95 ng/mL, demonstrating both sensitivity and selectivity. The recoveries of this aptasensor in water samples ranged from 90 to 109.9%, which was quite in line with high-performance liquid chromatography. These findings suggest that the aptasensor is a valuable tool for detecting SQX in aqueous environmental samples.

Sensitive Detection of Escherichia coli O157:H7 Using Allosteric Probe and Hairpin Switches-Based Isothermal Transcription Amplification

Pathogens pose a serious threat to public and population health, leading to serious outbreak and spread of diseases irrespective of the region. The capability to directly, sensitively, and specifically detect viable pathogens in low numbers in food and clinical samples is very desirable but remains a challenge. In this work, we present a novel assay of a combination of an aptamer-based allosteric probe and hairpin switch-controlled T7 RNA polymerase-based isothermal transcription amplification, which enables rapid, ultrasensitive, label-free detection of direct pathogens. It can detect Escherichia coli as low as 73.2 CFU/mL. Moreover, with the usage of the proposed assay, sensitive quantification of E. coliO157:H7 in milk samples has been achieved, showing significant potential as a simple and sensitive tool to quantify pathogens in milk and other foods.

A colorimetric platform for sensitive sensing of Hg2+ and S2- based on Se-AuNPs with Hg2+-activated peroxidase-like activity

Herein, the selenium (Se) modified gold nanoparticles (Se-AuNPs) was synthesized using cerium doped carbon dots (Ce-CDs) as a reducing agent and template. As desired, Se-AuNPs displays enhanced peroxidase (POD)-like activity in the presence of Hg2+. The mechanism for the enhanced activity was attributed to the increased affinity between Se-AuNPs-Hg2+ and the substrate, in which Se and Au elements have a strong binding capacity to Hg2+, forming Hg-Se bonds and Au-Hg amalgam to generate more ·OH. This POD-like activity of Se-AuNPs-Hg2+ correlates with the colorimetric reaction by the catalytic reaction between 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2. The oxidation of TMB was completely inhibited by the introduction of the reductive S2-. Based on the above findings, a strategy for the colorimetric detection of Hg2+ and S2- by Se-AuNPs was established with linear ranges of 0.33-66 μg/L and 0.625-75 μg/L, and low detection limits of 0.17 μg/L and 0.12 μg/L (3.3 δ/k), respectively. When the colorimetric probes for detection of Hg2+ and S2- was applied in environmental water samples, the recoveries were in the range of 90.3-108.0 %. This method will provide a new idea for the colorimetric detection strategy of Hg2+ due to the strong interaction between Hg and Se.

Advances in magnetic analytical extraction techniques for detecting antibiotic residues in edible samples

The widespread use of antibiotics in agricultural and animal husbandry to treat bacterial illnesses has resulted in a rise in antibiotic-resistant bacteria. These bacteria can grow when antibiotic residues are present in food items, especially in edible animal products. As a result, it is crucial to monitor and regulate the amounts of antibiotics in food. Magnetic analytical extractions (MAEs) have emerged as a potential approach for extracting antibiotic residues from food using magnetic nanoparticles (MNPs). Recent improvements in MAEs have resulted in the emergence of novel MNPs with better selectivity and sensitivity for the extraction of antibiotic residues from food samples. Consequently, this review paper addresses current developments in MAE for extracting antibiotic residues from edible samples. It also provides a critical analysis of contemporary MAE practices. The current issues and potential future developments in this field are also discussed, thereby providing a framework for future study paths.

Detection of proteins with ascorbic acid-capped gold nanoparticles: a simple and highly sensitive colorimetric assay

We report a simple and highly sensitive colorimetric method for the detection and quantification of proteins, based on the aggregation of ascorbic acid (AA) capped gold nanoparticles (AuNPs) by proteins. The interactions between our AuNPs and nine different proteins of various sizes and shapes (cytochrome C (12 kDa), lysozyme (14.3 kDa), myoglobin (17 kDa), human serum albumin (66 kDa), bovine serum albumin (66.4 kDa), human transferrin (80 kDa), aldolase (160 kDa), catalase (240 kDa), and human H-ferritin (500 kDa)) generated similar AuNPs-protein absorption spectra in a concentration-dependent manner in the range of 1-15 nM. Upon the addition of a protein, the UV-visible spectra of AuNPs-protein conjugates shifted from 524 nm for the AuNps alone to longer wavelength (600-750 nm) due to the presence of one of these proteins. This bathochromic shift is accompanied by a color change from a cherry red, to dark purple, and then light grey or colorless if excess protein has been added, indicating the formation of AuNPs-protein conjugates followed by protein-induced aggregation of the AuNPs. High-resolution transmission electron microscopy images revealed uniformly distributed spherical nanoparticles with an average size of 27.5 ± 15.2 nm, increasing in size to 39.6 ± 12.9 nm upon the addition of a protein, indicating the formation of AuNPs-protein conjugates in solution. A general mechanism for the protein-induced aggregation of our AuNPs is proposed. The consistent behavior observed with the nine proteins tested in our study suggests that our assay can be universally applied for the quantification of pure proteins in a solution, regardless of size, shape, or molecular weight.

Ag-modified CuO cavity arrays as a SERS-electrochemical dual signal platform for thiram detection

Rapid and sensitive determination of pesticide residues in fruits and vegetables is critical for human health and ecosystems. This paper used an Ag-modified CuO sphere-cavity array (CuO@Ag) electrode as a thiram SERS/electrochemical dual readout detection platform. Numerous Raman "hotspots" generated by uniformly distributed silver nanoparticles, charge transfer at the CuO@Ag interface, and the formation of Ag-thiram complexes contribute to the significant enhancement of this SERS substrate, which results in excellent SERS performance with an enhancement factor up to 1.42 × 106. When using SERS as the readout technique, the linear range of the substrate for thiram detection was 0.05-20 nM with a detection limit (LOD) of up to 0.0067 nM. Meanwhile, a correlation between the value of change in current density and thiram concentration was established due to the formation of stable complexes of thiram with Cu2+ generated at specific potentials. The linear range of electrochemical detection was 0.05-20.0 μM, and the detection limit was 0.0167 μM. The newly devised dual-readout sensor offers notable sensitivity and stability. The two signal readout methods complement each other in terms of linear range and detection limit, making it a convenient tool for assessing thiram residue levels in agro-food. At the same time, the combination of commercially available portable equipment makes on-site monitoring possible.

Portable, intelligent MIECL sensing platform for ciprofloxacin detection using a fast convolutional neural networks-assisted Tb@Lu2O3 nanoemitter

Environmental pollution caused by ciprofloxacin is a major problem of global public health. A machine learning-assisted portable smartphone-based visualized molecularly imprinted electrochemiluminescence (MIECL) sensor was developed for the highly selective and sensitive detection of ciprofloxacin (CFX) in food. To boost the efficiency of electrochemiluminescence (ECL), oxygen vacancies (OVs) enrichment was introduced into the flower-like Tb@Lu2O3 nanoemitter. With the specific recognition reaction between MIP as capture probes and CFX as detection target, the ECL signal significantly decreased. According to, CFX analysis was determined by traditional ECL analyzer detector in the concentration range from 5 × 10-4 to 5 × 102 μmol L-1 with the detection limit (LOD) of 0.095 nmol L-1 (S/N = 3). Analysis of luminescence images using fast electrochemiluminescence judgment network (FEJ-Net) models, achieving portable and intelligent quick analysis of CFX. The proposed MIECL sensor was used for CFX analysis in real meat samples and satisfactory results, as well as efficient selectivity and good stability.

Carbon-dots encapsulated luminescent metal-organic frameworks@surface molecularly imprinted polymer: A facile fluorescent probe for the determination of chloramphenicol

In this study, carbon dots (CDs)-encapsulated luminescent metal-organic frameworks@surface molecularly imprinted polymer (CDs@MOF@SMIP) was facilely prepared and applied as fluorescent probe for specific identification and sensitive detection of chloramphenicol (CAP) in food. Fluorescent CDs, serving as signal tags, were encapsulated within metal-organic backbones (ZIF-8), yielding luminescent MOF materials (CDs@ZIF-8). The synthesized CDs, CDs@ZIF-8 and CDs@ZIF-8@SMIP were investigated by morphological and structural characterizations (UV-Vis, XRD, FT-IR, BET, TEM). The CDs@ZIF-8@SMIP probe was demonstrated to have remarkable selectivity and sensitivity towards CAP. Its fluorescence decreased linearly with CAP concentration from 0.323 μg L-1 (0.001 μM) to 8075.0 μg L-1 (25.0 μM), featuring a low detection limit of 0.08 μg L-1. The CDs@ZIF-8@SMIP-based fluorescence strategy achieved satisfactory recoveries (95.5 % - 101.0 %) in CAP-spiked commercial foods with RSD < 4.4 % (n = 3). These results indicate that this method can effectively detect trace CAP in food matrices and has broad application prospects.

Portable luminescent fiber- and glove-based nanosensor for multicolor visual detection of tetracycline in food samples

An intelligent fluorescent nanoprobe (lignite-CDs-Eu) was constructed by an effective and facile method based on lignite-derived carbon dots (CDs) and lanthanide europium ions (Eu3+), which exhibited high sensitivity, low detection limit (13.35 nM) and visual color variation (from blue to red) under ultraviolet light towards tetracycline (TC) detection. Significantly, portable and economical sensors were developed using lignite-CDs-Eu immobilized fiber material of filter paper and wearable glove with the aid of color extracting and image processing application (APP) in the smartphone. Facile, fast and real-time visual detection of TC in food samples was realized. Moreover, logic gate circuit was also designed to achieve intelligent and semi-quantitative inspection of TC. To some extent, this study extended the cross-application of intelligent computer software in food analytical science, and provided a certain reference for the development of small portable detection sensors which were suitable for convenience and non-professional use in daily life.

Enhancement of telomerase extension via quadruple nucleic acid recycling to develop a novel colorimetric biosensing method for kanamycin assay

BACKGROUND

Colorimetric biosensors have important value for antibiotic residue testing. However, many previous methods were constructed based on the optical density change of certain unstable single-colored products with poor discrimination for visual measurements. Moreover, their low extinction coefficients usually result in low sensitivity of biosensors. In addition, many conventional signal amplification strategies often involve sophisticated nanomaterial preparation, inconvenient multi-step assay manipulation and limited signal amplification ability. Therefore, the development of new colorimetric biosensing strategies with excellent visual discrimination, high sensitivity and convenient manipulation is highly desirable.

RESULTS

We designed a target recycling accelerated cascade DNA walking amplification mechanism to trigger a telomerase extension-related enzymatic reaction, and developed a novel colorimetric biosensing strategy for kanamycin (Kana) assay. The target recycling was induced by an exonuclease III-assisted aptamer recognition reaction, which could also trigger the successive DNA walking at the streptavidin (SA)- and magnetic bead (MB)-based tracks. This not only caused the quantitative exposure of the telomeric substrate primers on MB surfaces but also released another strand to accelerate the SA-based DNA walking. By using the telomerase extension product to link numerous alkaline phosphatases and induce the plasmonic property change of gold nanobipyramids (Au NBPs), a colorimetric signal output strategy was constructed. This method could be applied for the high-resolution visual screening of Kana, and it also showed a very low detection limit of 17.6 fg mL-1 for assaying Kana over a wide, five-order-magnitude linear range.

SIGNIFICANCE

The quadruple nucleic acid recycling-enhanced telomerase extension resulted in the ultrahigh sensitivity of the method and also excluded the sophisticated manipulations involved in conventional biosensing strategies. The multiple enzyme catalysis-induced plasmonic property change of Au NBPs realized the stable and multicolor visual signal transduction. Together with its low cost, simple operation, high selectivity, excellent repeatability, and reliable performances, this method exhibits great potential for use in practical applications.

Dual Functional Ultrasensitive Point-of-Care Clinical Diagnosis Using Metal-Organic Frameworks-Based Immunobeads

Sepsis is an acute systemic infectious syndrome with high fatality. Fast and accurate diagnosis, monitoring, and medication of sepsis are essential. We exploited the fluorescent metal-AIEgen frameworks (MAFs) and demonstrated the dual functions of protein detection and bacteria identification: (i) ultrasensitive point-of-care (POC) detection of sepsis biomarkers (100 times enhanced sensitivity); (ii) rapid POC identification of Gram-negative/positive bacteria (selective aggregation within 20 min). Fluorescent lateral flow immunoassays (LFAs) are convenient and inexpensive for POC tests. MAFs possess a large surface area, excellent photostability, high quantum yield (∼80%), and multiple active sites serving as protein binding domains for ultrasensitive detection of sepsis biomarkers (IL-6/PCT) on LFAs. The limit of detection (LOD) for IL-6/PCT is 0.252/0.333 pg/mL. Rapid appraisal of infectious bacteria is vital to guide the use of medicines. The dual-functional fluorescent MAFs have great potential in POC tests for the clinical diagnosis of bacterial infections.

Gold Nanoparticle-Based Colorimetric Sensors: Properties and Application in Detection of Heavy Metals and Biological Molecules

During the last decade, advances have been made in nanotechnology using nanomaterials, leading to improvements in their performance. Gold nanoparticles (AuNPs) have been widely used in the field of sensor analysis and are also combined with certain materials to obtain the desired characteristics. AuNPs are commonly used as colorimetric sensors in detection methods. In developing an ideal sensor, there are certain characteristics that must be met such as selectivity, sensitivity, accuracy, precision, and linearity, among others. Various methods for the synthesis of AuNPs and conjugation with other components have been carried out in order to obtain good characteristics for their application. AuNPs can be applied in the detection of both heavy metals and biological molecules. This review aimed at observing the role of AuNPs in its application. The synthesis of AuNPs for sensors will also be revealed, along with their characteristics suitable for this role. In the application method, the size and shape of the particles must be considered. AuNPs used in heavy metal detection have a particle size of around 15-50 nm; in the detection of biological molecules, the particle size of AuNPs used is 6-35 nm whereas in pharmaceutical compounds for cancer treatment and the detection of other drugs, the particle size used is 12-30 nm. The particle sizes did not correlate with the type of molecules regardless of whether it was a heavy metal, biological molecule, or pharmaceutical compound but depended on the properties of the molecule itself. In general, the best morphology for application in the detection process is a spherical shape to obtain good sensitivity and selectivity based on previous studies. Functionalization of AuNPs with conjugates/receptors can be carried out to increase the stability, sensitivity, selectivity, solubility, and plays a role in detecting biological compounds through conjugating AuNPs with biological molecules.

Development of Novel Peptide-Modified Silver Nanoparticle-Based Rapid Biosensors for Detecting Aminoglycoside Antibiotics

The detection and monitoring of aminoglycoside antibiotics (AGAs) have become of utmost importance due to their widespread use in human and animal therapy, as well as the associated risks of exposure, toxicity, and the emergence of antimicrobial resistance. In this study, we successfully synthesized casein hydrolysate peptides-functionalized silver nanoparticles (CHPs@AgNPs) and employed them as a novel colorimetric analytical platform to demonstrate remarkable specificity and sensitivity toward AGAs. The colorimetric and spectral response of the CHPs@AgNPs was observed at 405 and 520 nm, showing a linear correlation with the concentration of streptomycin, a representative AGA. The color changes from yellow to orange provided a visual indication of the analyte concentration, enabling quantitative determination for real-world samples. The AgNP assay exhibited excellent sensitivity with dynamic ranges of approximately 200-650 and 100-700 nM for streptomycin-spiked tap water and dairy whey with limits of detection found to be ∼98 and 56 nM, respectively. The mechanism behind the selective aggregation of CHPs@AgNPs in the presence of AGAs involves the amine groups of the target analytes acting as molecular bridges for electrostatic coupling with hydroxyl or carboxyl functionalities of adjacent NPs, driving the formation of stable NP aggregates. The developed assay offers several advantages, making it suitable for various practical applications. It is characterized by its simplicity, rapidity, specificity, sensitivity, and cost-effectiveness. These unique features make the method a promising tool for monitoring water quality, ensuring food safety, and dealing with emergent issues of antibiotic resistance.

Recent Advances of Biosensors for Detection of Multiple Antibiotics

The abuse of antibiotics has caused a serious threat to human life and health. It is urgent to develop sensors that can detect multiple antibiotics quickly and efficiently. Biosensors are widely used in the field of antibiotic detection because of their high specificity. Advanced artificial intelligence/machine learning algorithms have allowed for remarkable achievements in image analysis and face recognition, but have not yet been widely used in the field of biosensors. Herein, this paper reviews the biosensors that have been widely used in the simultaneous detection of multiple antibiotics based on different detection mechanisms and biorecognition elements in recent years, and compares and analyzes their characteristics and specific applications. In particular, this review summarizes some AI/ML algorithms with excellent performance in the field of antibiotic detection, and which provide a platform for the intelligence of sensors and terminal apps portability. Furthermore, this review gives a short review of biosensors for the detection of multiple antibiotics.

Chromogenic Mechanisms of Colorimetric Sensors Based on Gold Nanoparticles

The colorimetric signal readout method is widely used in visualized analyses for its advantages, including visualization of test results, simple and fast operations, low detection cost and fast response time. Gold nanoparticles (Au NPs), which not only exhibit enzyme-like activity but also have the advantages of tunable localized surface plasmon resonance (LSPR), high stability, good biocompatibility and easily modified properties, provide excellent platforms for the construction of colorimetric sensors. They are widely used in environmental monitoring, biomedicine, the food industry and other fields. This review focuses on the chromogenic mechanisms of colorimetric sensors based on Au NPs adopting two different sensing strategies and summarizes significant advances in Au NP-based colorimetric sensing with enzyme-like activity and tunable LSPR characteristics. In addition, the sensing strategies based on the LSPR properties of Au NPs are classified into four modulation methods: aggregation, surface modification, deposition and etching, and the current status of visual detection of various analytes is discussed. Finally, the review further discusses the limitations of current Au NP-based detection strategies and the promising prospects of Au NPs as colorimetric sensors, guiding the design of novel colorimetric sensors.

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.

Highly Sensitive Aptasensor for Detecting Cancerous Exosomes Based on Clover-like Gold Nanoclusters

Exosome-based liquid biopsy technologies play an increasingly prominent role in tumor diagnosis. However, the simple and sensitive method for counting exosomes still faces considerable challenges. In this work, the CD63 aptamer-modified DNA tetrahedrons on the gold electrode were used as recognition elements for the specific capture of exosomes. Partially complementary DNA probes act as bridges linking trapped exosomes and three AuNP-DNA signal probes. This clover-like structure can tackle the recognition and sensitivity issues arising from the undesired AuNP aggregation event. When cancerous exosomes are present in the system, the high accumulation of methylene blue molecules from DNA-AuNP nanocomposites on the surface of the electrode leads to an intense current signal. According to the results, the aptasensor responds to MCF-7 cell-derived exosomes in the concentration range from 1.0 × 10³ to 1.0 × 10⁸ particles·μL^-1, with the detection limit of 158 particles·μL^-1. Furthermore, the aptasensor has been extended to serum samples from breast cancer patients and exhibited excellent specificity. To sum it up, the aptasensor is sensitive, straightforward, less expensive, and fully capable of receiving widespread application in clinics for tumor monitoring.

Bio-Tailored Sensing at the Nanoscale: Biochemical Aspects and Applications

The demonstration of the first enzyme-based electrode to detect glucose, published in 1967 by S. J. Updike and G. P. Hicks, kicked off huge efforts in building sensors where biomolecules are exploited as native or modified to achieve new or improved sensing performances. In this growing area, bionanotechnology has become prominent in demonstrating how nanomaterials can be tailored into responsive nanostructures using biomolecules and integrated into sensors to detect different analytes, e.g., biomarkers, antibiotics, toxins and organic compounds as well as whole cells and microorganisms with very high sensitivity. Accounting for the natural affinity between biomolecules and almost every type of nanomaterials and taking advantage of well-known crosslinking strategies to stabilize the resulting hybrid nanostructures, biosensors with broad applications and with unprecedented low detection limits have been realized. This review depicts a comprehensive collection of the most recent biochemical and biophysical strategies for building hybrid devices based on bioconjugated nanomaterials and their applications in label-free detection for diagnostics, food and environmental analysis.

Gold Nanoparticles-Based Colorimetric Assays for Environmental Monitoring and Food Safety Evaluation

Recent years have witnessed an exponential increase in the research on gold nanoparticles (AuNPs)-based colorimetric sensors to revolutionize point-of-use sensing devices. Hence, this review is compiled focused on current progress in the design and performance parameters of AuNPs-based sensors. The review begins with the characteristics of AuNPs, followed by a brief explanation of synthesis and functionalization methods. Then, the mechanisms of AuNPs-based sensors are comprehensively explained in two broad categories based on the surface plasmon resonance (SPR) characteristics of AuNPs and their peroxidase-like catalytic properties (nanozyme). SPR-based colorimetric sensors further categorize into aggregation, anti-aggregation, etching, growth-mediated, and accumulation-based methods depending on their sensing mechanisms. On the other hand, peroxidase activity-based colorimetric sensors are divided into two methods based on the expression or inhibition of peroxidase-like activity. Next, the analytes in environmental and food samples are classified as inorganic, organic, and biological pollutants, and recent progress in detection of these analytes are reviewed in detail. Finally, conclusions are provided, and future directions are highlighted. Improving the sensitivity, reproducibility, multiplexing capabilities, and cost-effectiveness for colorimetric detection of various analytes in environment and food matrices will have significant impact on fast testing of hazardous substances, hence reducing the pollution load in environment as well as rendering food contamination to ensure food safety.

Metrological traceability in process analytical technologies and point-of-need technologies for food safety and quality control: not a straightforward issue

Traditional techniques for food analysis are based on off-line laboratory methods that are expensive and time-consuming and often require qualified personnel. Despite the high standards of accuracy and metrological traceability, these well-established methods do not facilitate real-time process monitoring and timely on-site decision-making as required for food safety and quality control. The future of food testing includes rapid, cost-effective, portable, and simple methods for both qualitative screening and quantification of food contaminants, as well as continuous, real-time measurement in production lines. Process automatization through process analytical technologies (PAT) is an increasing trend in the food industry as a way to achieve improved product quality, safety, and consistency, reduced production cycle times, minimal product waste or reworks, and the possibility for real-time product release. Novel methods of analysis for point-of-need (PON) screening could greatly improve food testing by allowing non-experts, such as consumers, to test in situ food products using portable instruments, smartphones, or even visual naked-eye inspections, or farmers and small producers to monitor products in the field. This requires the attention of the research community and devices manufacturers to ensure reliability of measurement results from PAT strategy and PON tests through the demonstration and critical evaluation of performance characteristics. The fitness for purpose of methods in real-life conditions is a priority that should not be overlooked in order to maintain an effective and harmonized food safety policy.

Laser-Printed Paper-Based Microfluidic Chip Based on a Multicolor Fluorescence Carbon Dot Biosensor for Visual Determination of Multiantibiotics in Aquatic Products

Excessive use of antibiotics in aquaculture severely endangers human health and ecosystems, which has raised significant concerns in recent years. However, conventional laboratory-based approaches regularly required time or skilled manpower. Herein, we propose a point-of-care-testing (POCT) biosensor detection device for the simultaneous determination of multiantibiotics without complex equipment or professional operators. A laser-printed paper-based microfluidic chip loaded with multicolor fluorescence nanoprobes (mCD-μPAD) was developed to rapidly detect sulfamethazine (SMZ), oxytetracycline (OTC), and chloramphenicol (CAP) on-site. These "fluorescence off" detection probes composed of carbon dots (CDs) conjugated with aptamers (donor) and MoS₂ nanosheets (acceptor) (CD-apt-MoS₂) were based on Förster resonance energy transfer. Upon the addition of target antibiotics, the significantly recovered fluorescence signal on the μPAD can be sensitively perceived by employing a 3D-printed portable detection box through a smartphone. Under optimal conditions, this μPAD allowed for a rapid response of 15 min toward SMZ, OTC, and CAP with considerable sensitivities of 0.47, 0.48, and 0.34 ng/mL, respectively. In shrimp samples, the recoveries were 95.2-101.2, 96.4-105, and 96.7-106.1% with RSD below 6%. This paper-based sensor opens an avenue for on-site, high-throughput, and rapid detection methods and can be widely used in POCT in food safety.

Coupled Gold Nanoparticles with Aptamers Colorimetry for Detection of Amoxicillin in Human Breast Milk Based on Image Preprocessing and BP-ANN

Antibiotic residues in breast milk can have an impact on the intestinal flora and health of babies. Amoxicillin, as one of the most used antibiotics, affects the abundance of some intestinal bacteria. In this study, we developed a convenient and rapid process that used a combination of colorimetric methods and artificial intelligence image preprocessing, and back propagation-artificial neural network (BP-ANN) analysis to detect amoxicillin in breast milk. The colorimetric method derived from the reaction of gold nanoparticles (AuNPs) was coupled to aptamers (ssDNA) with different concentrations of amoxicillin to produce different color results. The color image was captured by a portable image acquisition device, and image preprocessing was implemented in three steps: segmentation, filtering, and cropping. We decided on a range of detection from 0 µM to 3.9 µM based on the physiological concentration of amoxicillin in breast milk and the detection effect. The segmentation and filtering steps were conducted by Hough circle detection and Gaussian filtering, respectively. The segmented results were analyzed by linear regression and BP-ANN, and good linear correlations between the colorimetric image value and concentration of target amoxicillin were obtained. The R2 and MSE of the training set were 0.9551 and 0.0696, respectively, and those of the test set were 0.9276 and 0.1142, respectively. In prepared breast milk sample detection, the recoveries were 111.00%, 98.00%, and 100.20%, and RSDs were 6.42%, 4.27%, and 1.11%. The result suggests that the colorimetric process combined with artificial intelligence image preprocessing and BP-ANN provides an accurate, rapid, and convenient way to achieve the detection of amoxicillin in breast milk.

A label-free liquid crystal-assisted aptasensor for trace level detection of tobramycin in milk and chicken egg samples

Developed herein is an aptasensing array based on liquid crystal (LC) for monitoring of tobramycin (TOB) antibiotic. The direction of LC molecules from vertical to a random status was induced by the conformational changes of the specific aptamer due to its selective interaction with the target. The dark view of the aptasensing platform changed to colorful through observation by a polarized light microscope that clarifies the TOB presence. The aptasensor is especially able to determine TOB in the linear concentration range of 0.005-600 pM with a limit of detection (LOD) as 0.0021 pM. The TOB values can be determined successfully in the milk and chicken egg samples that highlights the potential applicability of the designed aptasensor. The proposed sensing approach is facile, operator-independent, label-free, and ultra-sensitive, making it novel for developing real-time portable sensing devices for future.

Zinc Ion-Based Switch-on Fluorescence-Sensing Probes for the Detection of Tetracycline

Tetracycline (TC) is an antibiotic that has been widely used in the animal husbandry. Thus, TC residues may be found in animal products. Developing simple and sensitive methods for rapid screening of TC in complex samples is of great importance. Herein, we demonstrate a fluorescence-sensing method using Zn²⁺ as sensing probes for the detection of TC. Although TC can emit fluorescence under the excitation of ultraviolet light, its fluorescence is weak because of dynamic intramolecular rotations, leading to the dissipation of excitation energy. With the addition of Zn²⁺ prepared in tris(hydroxymethyl)amino-methane (Tris), TC can coordinate with Zn²⁺ in the Zn²⁺-Tris conjugates to form Tris-Zn²⁺-TC complexes. Therefore, the intramolecular motions of TC are restricted to reduce nonradiative decay, resulting in the enhancement of TC fluorescence. Aggregation-induced emission effects also play a role in the enhancement of TC fluorescence. Our results show that the linear dynamic range for the detection of TC is 15-300 nM. Moreover, the limit of detection was ~7 nM. The feasibility of using the developed method for determination of the concentration of TC in a complex chicken broth sample is also demonstrated in this work.

Target-mediated competitive hybridization of hairpin probes for kanamycin detection based on exonuclease III cleavage and DNAzyme catalysis

Based on aptamer recognition and target-mediated competitive hybridization of hairpin probes, we developed a fluorescence sensor for kanamycin (KAN) detection. The aptamer and KAN binding will open hairpin H1 to release the trigger DNA fragment, which can initiate the competitive hybridization between hairpins H2 and H3. Then, exonuclease III (Exo III) can cleave H2 and H3 to produce numerous DNA3 and DNA4. Through the synergetic hybridization among DNA1, DNA2, DNA3, and DNA4, an active Mg²⁺-DNAzyme can be formed. The cleavage reaction toward FAM-BHQ-modified DNA2 will produce a high fluorescence signal for KAN assay. Through Exo III-guided cleavage and Mg²⁺-DNAzyme-based catalysis, the sensor exhibits high sensitivity, with a detection limit of 3.1 fM. This method is robust and has been applied to the detection of KAN in milk and water samples with good accuracy and reliability. Our developed fluorescence sensor exhibits the advantages of simple operation, high sensitivity, and good robustness, which are beneficial for KAN detection in food samples.

Smartphone based aptasensors as intelligent biodevice for food contamination detection in food and soil samples: Recent advances

Nowadays, the integration of conventional analytical approaches with smartphones has been developed novel, emerging and affordable devices for improving on-site detection platforms in the fields of food safety. Smartphone-based aptasensors as the next generation of portable aptasensing technique has attracted considerable attention as it offers a semi-automated user interface that can be exploited by inexpert characters. Wireless data transferability is an undeniable advantage that home-testing platforms have as well as it can suggest high computational power. In addition, these types of biodevices can provide real-time monitoring in terms of exchanging digital networks in real-time. To elaborate, the ability of smartphones to connect through the Internet is one of the most critical advantages of smartphone-based aptasensor that can be uploaded to Cloud databases and results can be disseminated as spatio-temporal maps across the globe. This review focused on the recent progress and technical breakthroughs of aptasensor on the smartphone as a groundbreaking enterprise in the field of biochemical analysis, importantly in the aspect of the combination of different types of biosensors including electrochemical, optical and colorimetric. In our opinion, this review can broaden our understanding of using smartphones as a portable sensing approach by addressing the current challenges and future perspectives.

Metal organic frameworks as advanced functional materials for aptasensor design

BACKGROUND

Advancement in coordination chemistry has achieved an impressive development of metal organic frameworks (MOFs) as the supramolecular hybrid materials, comprising harmonized metal nodes with organic ligands. Scope and approach: MOFs offer the unique properties of easy synthesis, nanoscale structure, adjustable size and morphology, high porosity, large surface area, supreme chemical tunability and stability, and biocompatibility. The features provide an exceptional opportunity for the widely usage of MOFs in the different scientific fields, e.g. biomedicine, electrocatalysis, food safety, energy storage, environmental surveillance, and biosensing platforms. The synergistic incorporation of the aptamer advantages and the superiorities of MOFs attains the novel MOF-based aptasensors. The excellent selectivity and sensitivity of the MOF-based aptasensors nominate them as efficient lab-on-chip tools for cost-effective, label-free, portable, and real-time monitoring of diverse targets.

KEY FINDINGS AND CONCLUSIONS

Here, we review the achievements in the sensor design by cooperation of MOF motifs and aptamers with the conspicuous potential of determining the targets. Finally, some results are expressed that provide a valuable viewpoint for developing the novel MOF-based test strips in the future.

When smartphone enters food safety: A review in on-site analysis for foodborne pathogens using smartphone-assisted biosensors

Pathogens are one of the supreme threats for the public health around the world in food supply chain. The on-site monitoring is an emerging trend for screening pathogens during the food processing and preserving. Traditional analytical tools have been unable to satisfy the current demands. Smartphones have enormous potentials for achieving on-site detection of foodborne pathogens, with intrinsic advantages such as small size, high accessibility, fast processing speed, and powerful imaging capacity. This review aims to synthesize the current advances in smartphone-assisted biosensors (SABs) for sensing foodborne pathogens, and briefly put forward the problem that consist in the research. We present the role of nanotechnology and recognition modes targeting foodborne pathogens in SABs, and discuss the signal conversion platforms coupling with smartphone. The challenges and perspectives in SABs are also proposed. The smartphone analytics area is moving forward, and it much be subject to careful quality standards and validation.

Colorimetric assay for tetracyclines based on europium ion-induced aggregation of gold nanoparticles

Oxytetracycline-capped gold nanoparticles (OTC-Au NPs) were prepared using sodium borohydride as the reductant and OTC as the capping agent, respectively. The prepared OTC-Au NPs with a size of 6 nm have a maximum surface plasma resonance (SPR) absorption located at 514 nm. The OTC on the surface of Au NPs still can coordinate with Eu³⁺ ions. Due to the property that OTC has multivalent binding sites with Eu³⁺ ions, Eu³⁺ ions can induce the aggregation of OTC-Au NPs. Based on the Eu³⁺ ions-aggregated OTC-Au NPs, a simple aptamer-free colorimetric sensing method for TCs was developed. Briefly, free TCs compete with OTC on the surface of Au NPs resulting in the change of OTC-Au NPs from an aggregation state to a dispersed state. The whole process takes only 5 min, and as low as 20 nM OTC, 14 nM tetracycline (TC), and 20 nM doxycycline (DC) could be sensitively detected, respectively. The proposed method was also featured as good repeatability and specificity, and was applied to the detection of OTC in lake water with satisfactory recovery.

A competitive colorimetric aptasensor for simple and sensitive detection of kanamycin based on terminal deoxynucleotidyl transferase-mediated signal amplification strategy

We developed a rapid and sensitive colorimetric biosensor based on competitive recognition between kanamycin (KAN), magnetic beads-kanamycin (MBs-KAN) and aptamer and terminal deoxynucleotidyl transferase (TdT)-mediated signal amplification strategy. In the absence of KAN, aptamers recognize MBs-KAN. TdT can amplify oligonucleotides to the 3'-OH ends of aptamers, with biotin-dUTP being embedded in the long single stranded DNA (ssDNA). Then the assay produced visual readout due to the horseradish peroxidase (HRP)-catalyzed color change of the substrate after the linkage between biotin and streptavidin (SA)-HRP. In the presence of KAN, however, aptamers tend to bind free KAN rather than MBs-KAN. In this case, aptamers are isolated by magnetic separation, resulting in the failure of signal amplification and catalytic signals. This competitive colorimetric sensor showed excellent selectivity toward KAN with the limit of detection (LOD) as low as 9 pM. And recovery values were between 93.8 and 107.8% when spiked KAN in milk and honey samples.

Colorimetric determination of tetracyclines based on aptamer-mediated dual regulation of gold nanoparticle aggregation and in situ silver metallization

A colorimetric assay was described for determination of tetracyclines (TCs) in complex matrices based on dual regulation of gold nanoparticle (AuNP) aggregation and in situ silver metallization. The reaction between p-aminophenol and silver ions (Ag⁺) catalyzed by aptamer (Apt)-functionalized AuNPs promoted the in situ deposition of Ag shells on AuNPs to afford core-shell bimetallic NPs (Au@AgNPs). When the target is present, Apt is separated from the AuNP surface through the Apt-target interaction. With the desorption of Apts, AuNPs catalyzed the formation of more aggregated Au@AgNPs with a thinner Ag shell, corresponding to the solution color gradually changing from orange-yellow to brown. Using A₆₀₀/A₄₁₀ as the determination signal, the assay gave visible linear relationships for TCs in the range of 0.3-6.0 μmol L^-1 with a detection limit (LOD) of 33.6 nmol L^-1. In particular, the assay was successfully applied to detect TCs in real samples with the recovery rate ranging from 91.2% to 106% and relative standard deviation (RSD) less than 4.6%. These results meet the requirements of sample analysis.

Recent advances in aptamer applications for analytical biochemistry

Aptamers are typically defined as relatively short (20-60 nucleotides) single-stranded DNA or RNA molecules that bind with high affinity and specificity to various types of targets. Aptamers are frequently referred to as "synthetic antibodies" but are easier to obtain, less expensive to produce, and in several ways more versatile than antibodies. The beginnings of aptamers date back to 1990, and since then there has been a continual increase in aptamer publications. The intent of the present account was to focus on recent original research publications, i.e., those appearing in 2019 through April 2020, when this account was written. A Google Scholar search of this recent literature was performed for relevance-ranking of articles. New methods for selection of aptamers were not included. Nine categories of applications were organized and representative examples of each are given. Finally, an outlook is offered focusing on "faster, better, cheaper" application performance factors as key drivers for future innovations in aptamer applications.

Gold nanoparticle-based optical nanosensors for food and health safety monitoring: recent advances and future perspectives

Modern society has been facing serious health-related problems including food safety, diseases and illness. Hence, it is urgent to develop analysis methods for the detection and control of food contaminants, disease biomarkers and pathogens. As the traditional instrumental methods have several disadvantages, including being time consuming, and having high cost and laborious procedures, optical nanosensors have emerged as promising alternative or complementary approaches to those traditional ones. With the advantages of simple preparation, high surface-to-volume ratio, excellent biocompatibility, and especially, unique optical properties, gold nanoparticles (AuNPs) have been demonstrated as excellent transducers for optical sensing systems. Herein, we provide an overview of the synthesis of AuNPs and their excellent optical properties that are ideal for the development of optical nanosensors based on local surface plasmon resonance (LSPR), colorimetry, fluorescence resonance energy transfer (FRET), and surface-enhanced Raman scattering (SERS) phenomena. We also review the sensing strategies and their mechanisms, as well as summarizing the recent advances in the monitoring of food contaminants, disease biomarkers and pathogens using developed AuNP-based optical nanosensors in the past seven years (2015-now). Furthermore, trends and challenges in the application of these nanosensors in the determination of those analytes are discussed to suggest possible directions for future developments.

The ultrathin palladium nanosheets for sensitive and visual Hg2+ detection in the food chain

The detection of mercury, one of the ten most dangerous chemicals, is significant to provide helpful information for assessing mercury toxicity and health risks. However, it is a challenge to explore simple, sensitive, accurate, and cheap Hg²⁺ detection methods. Noble metal nanomaterials are used for Hg²⁺ detection by the colorimetric method widely. Still, the pure noble metal materials' detection limit of Hg²⁺ is high, and sensitivity enhancement usually requires further complex modification. Here, we use a facile one-step route to synthesize ultra-thin two-dimensional palladium nanosheets (PdNS), which have high selectivity and sensitivity for Hg²⁺ detection by colorimetric method with a low detection limit (0.55 ppb). The detection of Hg²⁺ by PdNS involves multiple mechanisms, including the formation of amalgam and PdO to improve the peroxidase-mimic activity of PdNS and PdNS motor function to increase its collision probability with the detection reactant. The PdNS can be used to detect Hg²⁺ in various actual samples. The detection results are highly consistent with the data obtained by the atomic fluorescence spectrometer (AFS). Then, we developed a Hg²⁺ detection kit, which can realize simple, sensitive, and accurate Hg²⁺ detection by naked eye or cellphone at a meager cost (0.3 dollars each sample).

An Up-conversion signal probe-MnO2 nanosheet sensor for rapid and sensitive detection of tetracycline in food

The irrational use of tetracycline (TC) poses a serious threat to human health, which calls for the development of efficient and reliable detection methods. Herein, an ideal sensor based on luminescence resonance energy transfer (LRET) between aptamer modified up-conversion nanoparticles as signal probes (donors) and manganese dioxide (MnO₂) nanosheets (acceptors) was developed for TC detection in food samples. As a result of van der Waals forces between the nucleobases of the aptamer and the basal plane of MnO₂ nanosheets, the distance of the donors and acceptors was shortened. The emission spectrum of the signal probes and the absorption spectrum of MnO₂ nanosheets overlapped, resulting in LRET, and quenching of up-conversion luminescence. The TC-specific aptamer could fold into a complex conformational structure to provide recognition sites for TC. In the presence of TC, the aptamer was found to preferentially combine with TC due to the stacking of planar moieties, hydrogen bonding interactions and molecular shape complementarity, causing the separation of signal probes and nanosheets, and luminescence recovery. Consequently, a low detection limit of 0.0085 ng/mL was achieved with a wide detection range of 0.01-100 ng/mL. Moreover, the ability of the sensor to detect TC was confirmed in actual food samples and compared with the traditional ELISA with satisfactory results (p > 0.05).

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.

Europium Fluorescent Nanoparticles-Based Multiplex Lateral Flow Immunoassay for Simultaneous Detection of Three Antibiotic Families Residue

A fluorescent immunoassay based on europium nanoparticles (EuNPs-FIA) was developed for the simultaneous detection of antibiotic residues, solving the problems of single target detection and low sensitivity of traditional immunoassay methods. In the EuNPs-FIA, EuNPs were used as indictive probes by binding to anti-tetracyclines monoclonal antibodies (anti-TCs mAb), anti-sulphonamides monoclonal antibodies (anti-SAs mAb) and anti-fluoroquinolones monoclonal antibodies (anti-FQs mAb), respectively. Different artificial antigens were assigned to different regions of the nitrocellulose membrane as capture reagents. The EuNPs-FIA allowed for the simultaneous detection of three classes of antibiotics (tetracyclines, fluoroquinolones and sulphonamides) within 15 min. It enabled both the qualitative determination with the naked eye under UV light and the quantitative detection of target antibiotics by scanning the fluorescence intensity of the detection probes on the corresponding detection lines. For qualitative analysis, the cut-off values for tetracyclines (TCs), fluoroquinolones (FQs) and sulphonamides (SAs) were 3.2 ng/ml, 2.4 ng/ml and 4.0 ng/ml, respectively, which were much lower than the maximum residue limit in food. For quantitative analysis, these ranged from 0.06 to 6.85 ng/ml for TCs, 0.03–5.14 ng/ml for FQs, and 0.04–4.40 ng/ml for SAs. The linear correlation coefficients were higher than 0.97. The mean spiked recoveries ranged from 92.1 to 106.2% with relative standard deviations less than 8.75%. Among them, the three monoclonal antibodies could recognize four types of TCs, seven types of FQs and 13 types of SAs, respectively, and the detection range could cover 24 antibiotic residues with different structural formulations. The results of the detection of antibiotic residues in real samples using this method were highly correlated with those of high performance liquid chromatography (R² > 0.98). The accuracy and precision of the EuNPs-FIA also met the requirements for quantitative analysis. These results suggested that this multiplex immunoassay method was a promising method for rapid screening of three families of antibiotic residues.

Gold nanoparticle-based colorimetric aptasensor for rapid detection of multiple mycotoxins in rice

A novel, simple and rapid colorimetric aptasensor for multiple mycotoxins (ochratoxin A (OTA) and aflatoxin B₁ (AFB₁)) detection was developed using unmodified gold nanoparticles (AuNPs). In the work, the high affinities of OTA and AFB₁ aptamers were employed as the recognition elements for the colorimetric determination of OTA and AFB₁. In the absence of mycotoxins, the sulfhydryl-modified aptamers were directly adsorbed to the AuNP surface through Au-S bonds, further prohibiting the aggregation induced by a high concentration of salt, and the solutions remain red. In the presence of mycotoxins, the corresponding aptamer-target complexes were formed and the corresponding aptamers were detached from the surface of AuNPs, leading to the aggregation of AuNPs under the optimal salt solution and a color change. By spectroscopic quantitative analysis and visual analysis, the LODs of OTA and AFB₁ were down to 0.005 ng mL^-1 and 0.07 ng mL^-1, respectively. Furthermore, the colorimetric aptasensor showed a high specificity in the presence of other interfering mycotoxins and metal ions. Finally, the developed aptasensor was applicable to detect OTA and AFB₁ in rice samples with satisfactory performance. Our strategy has great potential for the rapid and sensitive detection of OTA and AFB₁ for on-site analysis.

Development of gold nanoparticles-aptamer nanocomposite for multiplexed analysis of antibiotics and design of molecular logic gates

The widespread use of antibiotics caused severe problems of antibiotic residues in foodstuffs and water, posing a serious threat to public health and thus urging the development of sensitive, selective, and rapid detection methods for antibiotics. In this study, a fluorescence resonance energy transfer (FRET)-based system is developed for the multiplexed analysis of chloramphenicol (CAP) and streptomycin (Strep) with detection limits of 2.51 and 8.69μg l^-1, respectively. The FRET-based system consists of Cy3-tagged anti-CAP aptamer-conjugated gold nanoparticles (AuNPs) (referred to as AuNPs-AptCAP) and Cy5-tagged anti-Strep aptamer-conjugated AuNPs (referred to as AuNPs-AptStrep). In addition, AuNPs-AptCAP and AuNPs-AptStrep have been demonstrated to serve as signal transducers for implementing a series of logic operations such as YES, NOT, INH, OR, (2-4)-Decoder and even more complicated multi-level logic gates (OR-INH). Based on the outputs of logic operations, it could be figured out whether targeted analytes were present or not, thus enabling multiplex sensing and evaluation of pollution status. This proof of concept study might provide a new route for the enhanced sensing performance to distinguish different pollution status as well as the design of molecular mimics of logic elements to demonstrate better applicability.