Non-thiolated nucleic acid functionalized gold nanoparticle-based aptamer lateral flow assay for rapid detection of kanamycin

A novel dual-mode colorimetric and ratiometric fluorescence method for detecting isocarbophos based on S, N-CDs inhibiting Fe3O4@Cu-BTC nanozyme activity

Although many colorimetric methods have been developed for on-site pesticide detection, most exhibit low sensitivity and limited resistance to interference. To address these issues, this study developed a novel dual-mode colorimetric-ratiometric fluorescence method for isocarbophos (ICP) detection using sulfur and nitrogen co-doped carbon nanodots (S, N-CDs) to inhibit catalytic Fe3O4@Cu-BTC nanozyme activity. The synthesized Fe3O4@Cu-BTC nanozymes with higher peroxidase-like activity were inhibited by S, N-CDs. The inhibitory mechanism was deeply investigated and was ascribed to (1) the restriction of the reaction between Fe3O4@Cu-BTC and hydrogen peroxide (H2O2), which decreased the ·OH production, and (2) the ·OH scavenging ability of the S, N-CDs, forming the basis of the dual-mode method. The Fe3O4@Cu-BTC/Apt-complementary strand (CS)/S, N-CDs hybridization complexes demonstrated minimal to no peroxidase-like activity, preventing H2O2 from oxidizing o-phenylenediamine (OPD) to produce yellow fluorescent 2,3-diaminophenazine (DAP). Meanwhile, the detection system demonstrated a low fluorescence intensity ratio (I575/I465) at an excitation wavelength of 390 nm. However, the presence of ICP caused the CS/S, N-CDs to separate from the Fe3O4@Cu-BTC/Apt due to the high affinity between Apt and ICP. Then, the Fe3O4@Cu-BTC/Apt-ICP complexes recovered peroxidase-like activity, which promoted DAP production, accompanied by a pronounced fluorescence intensity ratio (I575/I465). In optimum conditions, the detection limits (LODs) were 2.79 ng/mL (colorimetric) and 0.26 ng/mL (ratiometric fluorescence), respectively. The feasibility of the proposed method was verified via three spiked samples, yielding recovery rates of between 86.08 % and 112.64 %, indicating the significant potential for the highly sensitive, accurate on-site detection of ICP in actual samples.

Nanoparticle-mediated light-driven LAMP combined with test strips for sensitive and rapid visual detection of antibiotic resistance genes

Antibiotic resistance genes (ARGs) are markers of drug-resistant pathogens, monitoring them contributes to prevent resistance to drugs. The detection methods for ARGs including PCR and isothermal amplification are sensitive and selective. However, it may take several hours or cannot be used on spot. Here, a detection method was developed based on a novel nanoparticle-mediated light-driven (LD) loop-mediated isothermal amplification (LAMP) combining with test strips, and a commonly found methicillin-resistant gene mecA was analyzed to verify the method. Under laser irradiation, gold nanoparticles produced localized surface plasmon resonance. Therefore, they provided both light-induced electrons and localized heat, the former acted as the catalyst of LD-LAMP and the latter as the energy supply. The mecA was amplified, producing numerous double-labeled amplicons. The LD-LAMP was three times as efficient as metal-bathed LAMP. A visual test strip (TS) was designed based on sandwich lateral flow chromatography, reading a LAMP result within 5-10 min. The method has a detection limit of 13.8 copies/μL, with a linear range of 13.8 copies/μL∼1.38 × 107 copies/μL. The LD-LAMPTS was applied to the on-site detection of mecA in milk samples. The results were consistent with qPCR, and total detection time reduced from 1 h by qPCR to 20-25 min by LD-LAMPTS.

Simultaneous or separate detection of heavy metal ions Hg2+ and Ag+ based on lateral flow assays

A lateral flow assay (LFA) was developed for the simultaneous or separate detection of mercury ion and silver ion based on isothermal nucleic acid amplification. T-Hg2+-T and C-Ag+-C were utilized in the isothermal nucleic acid amplification strategy to form specific complementary base pairs. Under the action of KF polymerase and endonuclease Nt.BbvCl, trace amounts of Hg2+ and Ag+ were converted to Product-Hg2+ and Product-Ag+ as bridges. Biotin-labeled capture strands (Biotin-DNA1, Biotin-DNA1, and Biotin-DNA3) immobilized on the test strips could capture the Au NPs-DNA nanoprobes by hybridization with the generated bridge products for monitoring of two heavy metal ions simultaneously or separately. The assembly method of DNAs on the nanoprobes was explored, and the DNA sequences on the nanoprobes were designed so that only one kind of DNA strand was used to bind to all three capture DNA strands on the C, T1, and T2 bands. Under optimal detection conditions, the limits of detection for Hg2+ and Ag+ were 2.19 and 5.41 pM, respectively, with desired selectivity and reproducibility.

An innovative biosensor utilizing aptamer-gated mesoporous silica nanoparticles for determination of aminoglycoside antibiotics through indirect-lateral flow

BACKGROUND

Aminoglycoside antibiotics (AGs) are commonly utilized in both human and veterinary medicine to treat and manage a range of infections. These antibiotics are recognized for their narrow therapeutic window, with an overdose potentially resulting in severe side effects like kidney and ear damage. Hence, the implementation of a quick, precise, and on-the-spot testing method is crucial in clinical settings. In the present investigation, we designed an innovative indirect lateral flow assay (LFA) utilizing aptamers to detect kanamycin, a type of aminoglycoside antibiotics. We prepared mesoporous silica nanoparticles (MSNs) functionalized with amino groups, loaded them with morphine (MOP), and then sealed them with aminoglycoside aptamers (Apt). The complex of gated-MSNs@Apt was tested using the MOP LFA in the presence or absence of kanamycin antibiotics.

RESULTS

The indirect LFA system displayed a single colored line in the test line for positive samples, whereas it exhibited double colored lines in both the control line and test line for negative samples. Our custom-designed LFA biosensors demonstrated two linear ranges, from 10 nM to 350 nM and 500 nM-1500 nM, with a limit of detection (LOD) of 5 nM in serum media under optimized conditions. The introduced indirect LFA biosensor was effectively utilized to detect kanamycin, achieving a satisfactory recovery rate of 92.9-109.9 % with RSD of 1.68-7.73 % in serum samples.

SIGNIFICANCE

In general, the created LFA system offers a portable, straightforward, and affordable approach for point-of-care (POC) identification of kanamycin and other AGs.

Surface-Functionalizing Strategies for Multiplexed Molecular Biosensing: Developments Powered by Advancements in Nanotechnologies

Multiplexed biosensing methods for simultaneously detecting multiple biomolecules are important for investigating biological mechanisms associated with physiological processes, developing applications in life sciences, and conducting medical tests. The development of biosensors, especially those advanced biosensors with multiplexing potentials, strongly depends on advancements in nanotechnologies, including the nano-coating of thin films, micro-nano 3D structures, and nanotags for signal generation. Surface functionalization is a critical process for biosensing applications, one which enables the immobilization of biological probes or other structures that assist in the capturing of biomolecules. During this functionalizing process, nanomaterials can either be the objects of surface modification or the materials used to modify other base surfaces. These surface-functionalizing strategies, involving the coordination of sensor structures and materials, as well as the associated modifying methods, are largely determinative in the performance of biosensing applications. This review introduces the current studies on biosensors with multiplexing potentials and focuses specifically on the roles of nanomaterials in the design and functionalization of these biosensors. A detailed description of the paradigms used for method selection has been set forth to assist understanding and accelerate the application of novel nanotechnologies in the development of biosensors.

Combination of Capture-SELEX and Post-SELEX for procymidone-specific aptamer selection and broad-specificity aptamer discovery, and development of aptamer-based lateral flow assay

BACKGROUND

Due to its wide application, procymidone has become one of the pesticides with high detection rates in supervision and sampling. Therefore, it is necessary to establish a rapid and efficient method for the detection of procymidone. However, an important bottleneck restricting the development of rapid detection methods of procymidone is that its specific recognition elements are rarely reported. In this work, Capture-SELEX and post-SELEX were used in aptamer screening, and the obtained aptamers were used to construct an aptamer-based lateral flow assay (LFA).

RESULTS

Firstly, a specific aptamer Seq15 was obtained for procymidone by Capture-SELEX, and its dissociation constant (Kd) was 24.22 nM. Secondly, post-SELEX was used to analyze and modify Seq15 to improve its performance, and the Kd of the truncated sequence Seq15-2 was 21.28 nM. In addition to this, the broad-specificity aptamer Seq17-1 was obtained via post-SELEX. Seq17-1 could broadly recognize dicarboximide fungicides (procymidone, iprodione, chlozolinate, dimethachlon and vinclozolin) and their metabolic derivative (3,5-dichloroaniline). Finally, the specific aptamer-based LFA of procymidone was constructed, and the limit of detection (LOD) was 0.79 ng/mL. Meanwhile, the LODs of dicarboximide fungicides and their metabolic derivative were 0.62, 0.64, 0.71, 0.69, 0.64 and 0.66 ng/mL, respectively. The above LFAs were highly specific and stable, and had been successfully used for the detection of vegetable samples.

SIGNIFICANCE

Under the combination of Capture-SELEX and Post-SELEX, this study not only provides specific recognition elements for rapid detection of procymidone, but also provides new ideas for the discovery of broad-specificity aptamers. Combining broad-specificity primary detection and single-specificity quantification, a composite aptamer-based LFA detection platform has been developed, which significantly improves detection efficiency.

A comprehensive review of aptamer screening and application for lateral flow strip: Current status and future perspectives

The detection of biomarkers is of great significance for medical diagnosis, food safety, environmental monitoring, and agriculture. However, bio-detection technology at present often necessitates complex instruments, expensive reagents, specialized expertise, and prolonged procedures, making it challenging to fulfill the demand for rapid, sensitive, user-friendly, and economical testing. In contrast, lateral flow strip (LFS) technology offers simple, fast, and visually accessible detection modality, allowing real-time analysis of clinical specimens, thus finding widespread utility across various domains. Within the realm of LFS, the application of aptamers as molecular recognition probes presents distinct advantages over antibodies, including cost-effectiveness, smaller size, ease of synthesis, and chemical stability. In recent years, aptamer-based LFS has found extensive application in qualitative, semi-quantitative, and quantitative detection across food safety, environmental surveillance, clinical diagnostics, and other domains. This review provided a concise overview of different aptamer screening methodologies, selection strategies, underlying principles, and procedural, elucidating their respective advantages, limitations, and applications. Additionally, we summarized recent strategies and mechanisms for aptamer-based LFS, such as the sandwich and competitive methods. Furthermore, we classified LFSs constructed based on aptamers, considering the rapid advancements in this area, and discussed their applications in biological and chemical detection. Finally, we delved into the current challenges and future directions in the development of aptamer and aptamer-based LFS. Although this review was not thoroughly, it would serve as a valuable reference for understanding the research progress of aptamer-based LFS and aid in the development of new types of aptasensors.

Aptamer-modified paper-based analytical devices for the detection of food hazards: Emerging applications and future perspective

Food analysis plays a critical role in assessing human health risks and monitoring food quality and safety. Currently, there is a pressing need for a reliable, portable, and quick recognition element for point-of-care testing (POCT) to better serve the demands of on-site food analysis. Aptamer-modified paper-based analytical devices (Apt-PADs) have excellent characteristics of high portability, high sensitivity, high specificity, and on-site detection, which have been widely used and concerned in the field of food safety. The article reviews the basic components and working principles of Apt-PADs, and introduces their representative applications detecting food hazards. Finally, the advantages, challenges, and future directions of Apt-PADs-based sensing performance are discussed, to provide new directions and insights for researchers to select appropriate Apt-PADs according to specific applications.

Advances in Aptamer-Based Conjugate Recognition Techniques for the Detection of Small Molecules in Food

Small molecules are significant risk factors for causing food safety issues, posing serious threats to human health. Sensitive screening for hazards is beneficial for enhancing public security. However, traditional detection methods are unable to meet the requirements for the field screening of small molecules. Therefore, it is necessary to develop applicable methods with high levels of sensitivity and specificity to identify the small molecules. Aptamers are short-chain nucleic acids that can specifically bind to small molecules. By utilizing aptamers to enhance the performance of recognition technology, it is possible to achieve high selectivity and sensitivity levels when detecting small molecules. There have been several varieties of aptamer target recognition techniques developed to improve the ability to detect small molecules in recent years. This review focuses on the principles of detection platforms, classifies the conjugating methods between small molecules and aptamers, summarizes advancements in aptamer-based conjugate recognition techniques for the detection of small molecules in food, and seeks to provide emerging powerful tools in the field of point-of-care diagnostics.

A lateral flow strip for on-site detection of homocysteine based on a truncated aptamer

An elevated level of homocysteine (Hcy) in serum is closely related to the development of various diseases. Therefore, homocysteine has been widely employed as a biomarker in medical diagnosis and the on-site detection of homocysteine is highly desired. In this study, a truncated highly specific aptamer for homocysteine was screened and used to design a lateral flow strip (LFS) for the detection of homocysteine. The aptamer was derived from a previously reported sequence. Based on the result of molecular docking, the original sequence was subjected to truncation, resulting in a reduction of the length from 66 nt to 55 nt. Based on the truncated aptamer, the LFS was designed for the detection of homocysteine. In the presence of homocysteine, the aptamer selectively binds to it, releasing cDNA from the aptamer/cDNA duplex. This allows cDNA to bind to the capture probe immobilized on the T zone of the strip, resulting in a red signal on the T zone from gold nanoparticles (AuNPs). The strip enables the visual detection of homocysteine in 5 min. Quantitative detection can be facilitated with the aid of ImageJ software. In this mode, the linear detection range for homocysteine is within 5-50 μM, with a detection limit of 4.18 μM. The strip has been effectively utilized for the detection of homocysteine in human serum. Consequently, the combination of the truncated aptamer and the strip offers a method that is sensitive, quick, and economical for the on-site detection of homocysteine.

The Development of Aptamer-Based Gold Nanoparticle Lateral Flow Test Strips for the Detection of SARS-CoV-2 S Proteins on the Surface of Cold-Chain Food Packaging

The COVID-19 pandemic over recent years has shown a great need for the rapid, low-cost, and on-site detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this study, an aptamer-based colloidal gold nanoparticle lateral flow test strip was well developed to realize the visual detection of wild-type SARS-CoV-2 spike proteins (SPs) and multiple variants. Under the optimal reaction conditions, a low detection limit of SARS-CoV-2 S proteins of 0.68 nM was acquired, and the actual detection recovery was 83.3% to 108.8% for real-world samples. This suggests a potential tool for the prompt detection of SARS-CoV-2 with good sensitivity and accuracy, and a new method for the development of alternative antibody test strips for the detection of other viral targets.

Label-free "signal-off" PEC aptasensor for determination of kanamycin based on 3D nanoflower-like FeIn2S4/CdS Z-scheme heterostructures

Highly photoactive 3D nanoflower-like FeIn2S4/CdS heterostructures were synthesized by hydrothermal treatment and low-temperature cation exchange. The FeIn2S4/CdS displayed 14.5 times signal amplification in contrast to FeIn2S4 alone. It was applied as a photoactive substrate to construct a label-free photoelectrochemical (PEC) aptasensor for ultrasensitive determination of kanamycin (KAN). Under the optimal conditions, the constructed PEC aptasensor displayed a wide linear range (5.0 × 10-4 ~ 5.0 × 101 ng mL-1) and a low detection limit (S/N = 3) of 40.01 fg mL-1. This study provides some constructive insights for preparation of advanced photoactive materials and exhibits great potential for quantitative determination of antibiotics in foods and environmental samples.

A fluorescent aptasensor for ATP based on functional DNAzyme/walker and terminal deoxynucleotidyl transferase-assisted formation of DNA-AgNCs

The development of sensitive adenosine triphosphate (ATP) sensors is imperative due to the tight relationship between the physiological conditions and ATP levels in vivo. Herein, a fluorescent aptasensor for ATP is presented, which adopts a strategy that combines a split aptamer and a DNAzyme/walker with terminal deoxynucleotidyl transferase (TDT)-assisted formation of DNA-AgNCs to realize fluorescence detection of ATP. A multifunctional oligonucleotide sequence is rationally designed, which integrates a split aptamer, a DNAzyme and a DNA walker. Both multifunctional oligonucleotide and its substrate strand are connected to the surface of Fe₃O₄@Au nanoparticles via Au-S bonds. The existence of ATP can induce the formation of the complete aptamer, and then activate the DNAzyme to circularly cleave the substrate strand, leaving 2',3'-cyclophosphate at the 3'end of the strand. This blocks the polymerization of dCTP to form poly(C) even in the presence of TDT and dCTP, due to the lack of free 3'-OH. In contrast, when ATP is absent, the DNAzyme/walker cannot work and then TDT catalyzes the formation of poly(C) at the free 3'-OH of the substrate strand, which is subsequently utilized as the template to prepare DNA-AgNCs. The fluorescence response derived from AgNCs thus reflects the ATP concentration. Under the optimum conditions, the aptasensor shows a linear response range from 5 nM to 10 000 nM, with a detection limit of 0.27 nM. The level of ATP in human serum can be effectively measured by the aptasensor with good recovery, indicating its application potential in medical samples.

A fluorescent assay for sensitive detection of kanamycin by split aptamers and DNA-based copper/silver nanoclusters

Kanamycin was a group of essential antibiotics generally served in treating infections of animals which leached into the environment residual in food, causing health concerns. Thus, selective and sensitive monitoring of kanamycin was significant for food safety. In this work, split aptamers were used as templates to prepare fluorescent Cu/Ag NCs for detection of kanamycin. According to the impressive affinity of the aptamer to kanamycin, two different detection modes were designed using kanamycin aptamer as a recognition molecule, in which one was to combine split aptamer Apt-1 with Apt-2 to form an entangled DNA as a Cu/Ag NCs template, the other was to associate the normal aptamer after encirclement to form Cu/Ag NCs templates. After the addition of kanamycin, the fluorescence signals of the Cu/Ag NCs synthesized in the two modes were both enhanced, but the approach with split aptamer exhibited a superior observable sensitivity than that of the normal type. The detection range showed a well linear relationship between 80 nM and 10 μM when the emission wavelength was 560 nm, and the detection limit was 13.3 nM. In addition, when streptomycin, oxytetracycline, chloramphenicol and chlortetracycline were involved in the selective interference experiment under the same conditions, the fluorescence intensity of the system performed no significant changes. The results demonstrated that this method possessed favorable specificity and selectivity for the assay of kanamycin, proficiently achieving efficient, rapid and sensitive evaluation of kanamycin in the milk samples.

A highly sensitive lateral flow immunoassay for the rapid and on-site detection of enrofloxacin in milk

Enrofloxacin (ENR) is a veterinary antibiotic used to treat bacterial infections in livestock. It chiefly persists in foods and dairy products, which in turn pose severe risks to human health. Hence it is very important to detect the ENR in foods and dairy products to safeguard human health. Herein, we attempted to develop a single-step detection lateral flow immunochromatographic assay (LFIA) using gold nanoparticles (AuNPs) for the rapid and on-site detection of ENR in milk samples. An anti-enrofloxacin monoclonal antibody (ENR-Ab) was conjugated with AuNPs for the specific detection of ENR in milk samples. For sensitivity improvement, many optimization steps were conducted on LFIA test strips. The visual limit of detection (vLOD) was found to be 20 ng/ml with a cut-off value of 50 ng/ml in the milk samples. The obtained LOD and cut-off value were within the safety limit guidelines of the Ministry of food and drug safety, South Korea. The test strip showed negligible cross-reactivity with ENR analogs, and other components of antibiotics, this indicates the high specificity of the LFIA test strip towards ENR. The designed test strip showed good reliability. The visual test results can be seen within 10 min without the need for special equipment. Therefore, the test strip can be employed as a potential detection strategy for the qualitative on-site detection of enrofloxacin in milk samples.