Rapid detection of clenbuterol in milk using microfluidic paper-based ELISA

Electrochemical biosensors: The beacon for food safety and quality

Electrochemical biosensors transduce chemical reactions into measurable electrical signals by incorporating recognition components. Although they are capable of detecting a broad range of target molecules, their application in complex matrices, such as food, at minimum or no sample preparation, is challenging and requires the introduction of innovative and effective strategies. This review explores the recent advances in electrochemical biosensors for on-site food safety and quality analysis. We first discuss the presence of chemical contaminants and biohazards in food and the need for robust, rapid, low-cost, and point-of-care (POC) analytical techniques. We then address the critical aspects of sensitivity and selectivity of electrochemical biosensors in detecting chemical and biological contaminants in real food samples. We finally investigate the major drawbacks of these biosensors and provide future perspectives on the field.

Origami Paper-Based Immunoassay Device with CRISPR/Cas12a Signal Amplification

In clinical diagnosis, the determination of target proteins at low concentration levels is generally performed by immunoassays, such as the enzyme-linked immunosorbent assay (ELISA), which is a time-consuming process. To date, paper-based ELISA platforms enabling faster and less expensive analysis have been developed, but their important issue for clinical applications is the limited sensitivity compared to conventional ELISA. To address this challenge, this paper introduces a simple, rapid, and highly sensitive detection method for non-nucleic acid targets achieved by integrating the CRISPR/Cas12a system into paper-based ELISA. An origami-type paper-based device enabling simple assay operation has been designed, and the detection of targets on the paper substrates is based on observing the fluorescence signal induced by the CRISPR/Cas12a enzyme cleaving a probe single-stranded DNA (ssDNA) labeled with fluorophore and quencher (FQ reporter). To enhance sensitivity, antibodies labeled with a network of multiple DNA activating the CRISPR/Cas12a enzyme have been utilized as detection antibodies. As a result, the developed device successfully boosted the detection sensitivity for both human IgG and the hepatitis B virus surface antigen (HBsAg). In particular, the limit of detection (LOD) for HBsAg was estimated to be 12 pg/mL, representing over 10-fold higher sensitivity compared with commercially available HBsAg ELISA kits (LOD: 200 pg/mL). In addition, the fluorescence response toward porcine whole blood samples containing different HBsAg concentrations was also confirmed by capturing images with a smartphone, followed by quantitative data analysis. These results demonstrate the potential applicability of the proposed platform for clinical tests at the point of care.

The development and application of SERS-based lateral flow immunochromatography in the field of food safety

Surface-Enhanced Raman Scattering-Lateral Flow Immunoassay (SERS-LFIA) inherits the advantages of simplicity, rapidness, and stability from Lateral Flow Immunoassay (LFIA), while integrating the sensitivity and accuracy of SERS, thereby attracting extensive attention in the field of food safety monitoring. This paper delves into the design strategies and principles underlying SERS-LFIA, introducing the detection formats based on SERS and contrasting the differences between traditional Raman molecules and those located in the Raman-silent region. It analyzes two immunoassay methods, namely sandwich and competitive, along with their respective applications. Importantly, by reviewing the applications of SERS-LFIA in food safety monitoring over the past 5 years, this paper summarizes the challenges faced by SERS-LFIA technology in practical applications and development. Furthermore, it provides a forward-looking perspective on the future development of SERS-LFIA. As a pivotal analytical method in the field of food safety monitoring, SERS-LFIA is demonstrating immense potential. It is hoped that this paper will offer valuable insights for the future development and application of SERS-LFIA.

Asymmetric CRISPR-Cas12a powered electrochemical aptasensor for clenbuterol detection based on competitive gRNA mediated cascade signal amplification

The residue of clenbuterol (CLB) in food poses a potential harm to human health. Herein, we presented an electrochemical aptasensor (E-A-CRISPR) based on employing an aptamer as a specific recognition element and asymmetric CRISPR-Cas12a as signal amplifiers for sensitive, and selective detection of CLB. In this E-A-CRISPR system, the target CLB bound to the aptamer and initiated cascade signal amplification through the DNase activity of CRISPR-Cas12a with two competitive gRNAs. Upon amplification, the active Cas12a cleaved the methylene blue-labeled hairpin probe on the electrode, reducing the peak current. Under optimal conditions, the E-A-CRISPR system showed a wide linear range (1 pM-100 nM) and a low detection limit (500 fM). This system could detect CLB in potable water, pig liver, and pork samples, showing significant potential for food safety monitoring. To our knowledge, this study is the first to use a CRISPR-Cas12a powered system for electrochemical sensing of CLB.

One simple and integrated nano-inspection platform for high-throughput detection of clenbuterol

To achieve high throughput detection of clenbuterol while reducing matrix interference, we developed a simple and integrated nano-inspection platform. Herein, based on the simplicity and convenience of paper chip, a multi-layer paper chip-chemiluminescence (CL) sensor was designed in the form of "48-well plate" type. The all-in-one paper chip-CL sensor has integrated the covalent organic frameworks (COFs) layer for sample matrix purification, high affinity nanobody layer for specific capture of target, and CL rapid response layer for the final determination. The signal readout was realized by the inhibitory effect of clenbuterol on the K3[Fe(CN)6] CL system. Detection of clenbuterol in pork meat was verified by measuring the CL intensity and satisfactory recoveries (85.9 %-97.3 %) were achieved. 48 samples could be simultaneously detected on one-chip in one-test, favoring the high-throughput detection. Especially, the work explored a new pathway for design of portable analytical instruments to achieve immediate on-site detection of hazards.

A clenbuterol detection method based on magnetic separation up-conversion fluorescent probe

In this study, a fluorescence detection method combining aptamer-modified up-conversion nanoparticles (UCNPs) and magnetic nanoparticles (MNPs) was developed for detection of Clenbuterol (CLB). The aptamer-modified magnetic NPs captured CLB, which reacted with the aptamer-modified UCNPs and generated a sandwich complex. The aptamer-modified UCNPs acted as a fluorescence source. The MNP-CLB-UCNP complex was retrieved from the solution using an magnetic field, and the fluorescence intensity was detected by fluorescence spectrophotometry with excitation and emission spectra at 980 nm and in the 400-800 nm region, respectively. The results showed that the fluorescence intensity gradually increased with increasing concentrations of CLB with a good specify. The method was highly sensitive for the quantification of CLB, with a limit of detection of 0.304 ng mL-1. The recovery rate of CLB from pork samples ranged from 84 % to 94.87 %. This fluorescence method enables the sensitive, precise, and accurate quantification of CLB residues in pork samples.

Comparison of protein immobilization methods with covalent bonding on paper for paper-based enzyme-linked immunosorbent assay

In this study, two methods were examined to optimize the immobilization of antibodies on paper when conducting a paper-based enzyme-linked immunosorbent assay (P-ELISA). Human IgG, as a test-capture protein, was immobilized on paper via the formation of Schiff bases. Aldehyde groups were introduced onto the surface of the paper via two methods: NaIO4 and 3-aminopropyltriethoxysilane (APTS) with glutaraldehyde (APTS-glutaraldehyde). In the assay, horseradish peroxidase-conjugated anti-human IgG (HRP-anti-IgG) binds to the immobilized human IgG, and the colorimetric reaction of 3,3',5,5'-tetramethylbenzyzine (TMB) produces a blue color in the presence of H2O2 and HRP-anti-IgG as a model analyte. The immobilization of human IgG, the enzymatic reaction conditions, and the reduction of the chemical bond between the paper surface and immobilized human IgG all were optimized in order to improve both the analytical performance and the stability. In addition, the thickness of the paper was examined to stabilize the analytical signal. Consequently, the APTS-glutaraldehyde method was superior to the NaIO4 method in terms of sensitivity and reproducibility. Conversely, the reduction of imine to amine with NaBH4 proved to exert only minimal influence on sensitivity and stability, although it tended to degrade reproducibility. We also found that thick paper was preferential when using P-ELISA because a rigid paper substrate prevents distortion of the paper surface that is often caused by repeated washing processes.

Development of a smartphone-integrated microfluidic paper-based optosensing platform coupled with molecular imprinting technique for in-situ determination of histamine in canned tuna

We reported the development of a smartphone-integrated microfluidic paper-based optosensing platform for in-situ detection and quantification of histamine in canned tuna. Molecularly imprinted polymers were synthesized via precipitation polymerization and utilized as dispersive solid phase extraction sorbent to selectively extract histamine from canned tuna. Carbon quantum dots functioning as a fluorescent probe were synthesized and introduced onto the microzones of the microfluidic paper device. This facilitated a noticeable fluorescence color change from dark red to vivid blue upon the addition of histamine. The change in fluorescence on the paper device was converted into specific RGB values using a portable UV light box combined with a smartphone. This assay achieved the limit of detection of 14.04 mg/kg with the linear range from 20 to 100 mg/kg of histamine in canned tuna. The entire molecular imprinting-microfluidic optosensing test could be completed in 45 min including sample preparation.

Open and closed microfluidics for biosensing

Biosensing is vital for many areas like disease diagnosis, infectious disease prevention, and point-of-care monitoring. Microfluidics has been evidenced to be a powerful tool for biosensing via integrating biological detection processes into a palm-size chip. Based on the chip structure, microfluidics has two subdivision types: open microfluidics and closed microfluidics, whose operation methods would be diverse. In this review, we summarize fundamentals, liquid control methods, and applications of open and closed microfluidics separately, point out the bottlenecks, and propose potential directions of microfluidics-based biosensing.

Paper-based sensors: affordable, versatile, and emerging analyte detection platforms

Paper-based sensors, often referred to as paper-based analytical devices (PADs), stand as a transformative technology in the field of analytical chemistry. They offer an affordable, versatile, and accessible solution for diverse analyte detection. These sensors harness the unique properties of paper substrates to provide a cost-effective and adaptable platform for rapid analyte detection, spanning chemical species, biomolecules, and pathogens. This review highlights the key attributes that make paper-based sensors an attractive choice for analyte detection. PADs demonstrate their versatility by accommodating a wide range of analytes, from ions and gases to proteins, nucleic acids, and more, with customizable designs for specific applications. Their user-friendly operation and minimal infrastructure requirements suit point-of-care diagnostics, environmental monitoring, food safety, and more. This review also explores various fabrication methods such as inkjet printing, wax printing, screen printing, dip coating, and photolithography. Incorporating nanomaterials and biorecognition elements promises even more sophisticated and sensitive applications.

Microfluidic paper analytic device (μPAD) technology for food safety applications

Foodborne pathogens, food adulterants, allergens, and toxic chemicals in food can cause major health hazards to humans and animals. Stringent quality control measures at all stages of food processing are required to ensure food safety. There is, therefore, a global need for affordable, reliable, and rapid tests that can be conducted at different process steps and processing sites, spanning the range from the sourcing of food to the end-product acquired by the consumer. Current laboratory-based food quality control tests are well established, but many are not suitable for rapid on-site investigations and are costly. Microfluidic paper analytical devices (μPADs) are a fast-growing field in medical diagnostics that can fill these gaps. In this review, we describe the latest developments in the applications of microfluidic paper analytic device (μPAD) technology in the food safety sector. State-of-the-art μPAD designs and fabrication methods, microfluidic assay principles, and various types of μPAD devices with food-specific applications are discussed. We have identified the prominent research and development trends and future directions for maximizing the value of microfluidic technology in the food sector and have highlighted key areas for improvement. We conclude that the μPAD technology is promising in food safety applications by using novel materials and improved methods to enhance the sensitivity and specificity of the assays, with low cost.

Improving pesticide residue detection: Immobilized enzyme microreactor embedded in microfluidic paper-based analytical devices

Orientationally immobilized enzyme microreactors (OIMERs), embedded in microfluidic paper-based analytical devices (μPADs) were developed for improved detection of pesticide residues in food. Acetylcholinesterase (AChE) was orientationally immobilized on the reusable Part I of the μPADs, using the specific affinity binding of concanavalin A (Con A) to a glycosyl group on AChE. Using the disposable Part II, facile colorimetric quantification was performed with a smartphone and software, or qualitative detection by a naked-eye visual test. The AChE immobilized in OIMERs not only had improved activity and stability, but also high sensitivity, with a limit of detection as low as (0.007 ± 0.003) μg/mL. The method was used to detect pesticides residues in real vegetable samples; the recovery (88.6-102.7%) showed high reliability for pesticide residues detection in foods. A molecular docking study and an enzyme kinetic analysis were conducted to characterize the mechanism of action of the OIMERs.

Non-enzymatic paper-based analytical device for direct potentiometric detection of urine creatinine

A paper-based analytical device (PAD) with an integrated composite electrode has been designed and fabricated for non-enzymatic creatinine sensing. Reduced graphene oxide (rGO) was employed to modify the PAD so that it could function as a solid-contact transducer. A new macrocyclic pyrido-hexapeptide derivative was made and used as a special ionophore in the creatinine membrane sensor. The synthesized PAD showed a detection limit of 1.0 µM (S/N = 3) and a potentiometric response towards creatinine throughout a log-linear range of 2.0 µM-10 mM (R2 = 0.9998). The sensor shows significant selectivity for a few related substances, including ephedrine, codeine, ketamine, caffeine, urea, urate, carbinoxamine, and dextromethorphan. It has been established that the testing method is appropriate for the direct potentiometric detection of creatinine in a variety of human urine sample types. When an indicating electrode and a reference electrode are put on the same flexible disposable, this lets applications with a small sample volume be done. For point-of-care creatinine measurement, the developed paper-based analytical equipment is a good choice because it is affordable, easily accessible, and self-pumping (especially when combined with potentiometric detection).

A portable microfluidic photometric detection method based on enzyme linked immunoscatter enhancement

Currently, the combination of smart phones and microfluidic chips is a commonly used device for point-of-care testing (POCT) detection. Enzyme linked immunosorbent assay (ELISA) is an effective way to detect specific proteins in disease. Because the detection accuracy of smartphone cameras is difficult to directly replace high-precision spectral devices, the combination of smartphones and ELISA has not been widely used. Therefore, this paper proposes a microfluidic photometric detection method based on ELISA scattering enhancement. Firstly, the scattering characteristics of IMB are mined, and the optimal value of absorbance error compensation parameter is obtained. Secondly, the absorbance error compensation model based on scattering enhancement characteristics is established to improve the image acquisition accuracy of smart phones. Finally, the microfluidic photometric detection chip is developed, and the optical path system, optical path adjustment system and POCT detection App of smart phone are designed. The optimal compensation parameters of IMB were obtained based on simulated samples, and the linearity of absorbance and concentration increased by 22.6% after compensation. In the IL-6 sample experiment, the detection results of the platform in this paper had a good linear correlation with IL-6 sample concentration, and the linear correlation coefficient was above 0.95459. At the same time, the detection limit and accuracy meet the detection requirements. Therefore, with the participation of smart phones and microfluidic chips, problems such as difficult carrying and complex operation in traditional ELISA daily detection have been solved, laying a foundation for the future promotion and application of ELISA based POCT platform.

Mesoporous silica-stabilized magnetite nanoparticles with peroxidase-like activities for sensitively detecting cholesterol in animal-derived foods

Sensitive detection of cholesterol in animal-derived foods is crucial for maintaining human healthy diets. In this study, an elegant approach utilizing inorganic nanozyme-based magnetic mesoporous silica nanoparticles (MMSNs) for the highly sensitive detection of cholesterol in animal-derived food products was reported. The results revealed the fabricated MMSNs exhibited remarkably intrinsic peroxidase (POD)-like catalytic activities with improved affinity, and the catalytic behavior aligned well with Michaelis-Menten equation. In addition, the data indicated that the MMSNs enabled visual colorimetric detection of cholesterol with a remarkably low detection limit of 7.12 μM by combining catalytic oxidation with cholesterol oxidase (ChOx). Furthermore, the prepared MMSNs were successfully employed for assessing cholesterol content in milk and egg yolk samples, indicating potential applications for cholesterol detection in animal-derived foods in future.

Microfluidic advances in food safety control

Food contamination is a global concern, particularly in developing countries. Two main types of food contaminants-chemical and biological-are common problems that threaten human health. Therefore, rapid and accurate detection methods are required to address the threat of food contamination. Conventional methods employed to detect these two types of food contaminants have several limitations, including high costs and long analysis time. Alternatively, microfluidic technology, which allows for simple, rapid, and on-site testing, can enable us to control food safety in a timely, cost-effective, simple, and accurate manner. This review summarizes advances in microfluidic approaches to detect contaminants in food. Different detection methods have been applied to microfluidic platforms to identify two main types of contaminants: chemical and biological. For chemical contaminant control, the application of microfluidic approaches for detecting heavy metals, pesticides, antibiotic residues, and other contaminants in food samples is reviewed. Different methods including enzymatic, chemical-based, immunoassay-based, molecular-based, and electrochemical methods for chemical contaminant detection are discussed based on their working principle, the integration in microfluidic platforms, advantages, and limitations. Microfluidic approaches for foodborne pathogen detection, from sample preparation to final detection, are reviewed to identify foodborne pathogens. Common methods for foodborne pathogens screening, namely immunoassay, nucleic acid amplification methods, and other methods are listed and discussed; highlighted examples of recent studies are also reviewed. Challenges and future trends that could be employed in microfluidic design and fabrication process to address the existing limitations for food safety control are also covered. Microfluidic technology is a promising tool for food safety control with high efficiency and applicability. Miniaturization, portability, low cost, and samples and reagents saving make microfluidic devices an ideal choice for on-site detection, especially in low-resource areas. Despite many advantages of microfluidic technology, the wide manufacturing of microfluidic devices still demands intensive studies to be conducted for user-friendly and accurate food safety control. Introduction of recent advances of microfluidic devices will build a comprehensive understanding of the technology and offer comparative analysis for future studies and on-site application.

A determination method for clenbuterol residue in pork based on optimal particle size gold colloid using SERS

Clenbuterol is often used as a feed additive to increase the percentage of lean meat in livestock. Meat containing clenbuterol can cause many illnesses and even death for people. In this paper, the particle growth method was used to prepare gold colloids of different sizes, and the enhanced effectiveness of gold colloids of different sizes on clenbuterol in pork was investigated. The results showed that the gold colloid with the best enhanced effectiveness for clenbuterol had a particle size of approximately 90 nm. Second, a sample collection component was designed to detect clenbuterol from bottom to top, solving the problem of poor reproducibility of Surface-enhanced Raman scattering (SERS) detection caused by different droplet sizes and shapes. Then, the influence of different volumes of samples and concentrations of aggregating compounds on the enhanced effectiveness was optimized. The results showed that, based on the sample collection components designed in this article, 5 µL of enhanced substrate, 7.5 µL of clenbuterol and 3 µL of 1 mol/L mixed detection of NaCl solution had the best enhanced performance. Finally, 88 pork samples (0.5, 1, 1.5,…, 10, 12, 14 µg/g) with different concentrations were divided into correction sets and prediction sets in a ratio of 3:1. Unary linear regression models were established between the concentration of clenbuterol residue in the pork and the intensity of the bands at 390, 648, 1259, 1472, and 1601 cm-1. The results showed that the unary linear regression models at 390, 648, and 1259 cm-1 had lower root mean square errors than those at 1472 and 1601 cm-1. The intensity of the three bands and the concentration of clenbuterol residue in the pork were selected to establish a multiple linear regression model, and the concentration of clenbuterol residue in the pork was predicted. The results showed that the determination coefficients (R2) of the correction set and the prediction set were 0.99 and 0.99, respectively. The root mean square errors (RMSE) of the correction set and the prediction set were 0.169 and 0.184, respectively. The detection limit of clenbuterol in pork by this method is 42 ng/g, which can realize the crude screening of pork containing clenbuterol in the market.

Capillary flow-driven immunoassay platform for COVID-19 antigen diagnostics

Over the last few years, the SARS-CoV-2 pandemic has made the need for rapid, affordable diagnostics more compelling than ever. While traditional laboratory diagnostics like PCR and well-plate ELISA are sensitive and specific, they can be costly and take hours to complete. Diagnostic tests that can be used at the point-of-care or at home, like lateral flow assays (LFAs) are a simple, rapid alternative, but many commercially available LFAs have been criticized for their lack of sensitivity compared to laboratory methods like well-plate ELISAs. The Capillary-Driven Immunoassay (CaDI) device described in this work uses microfluidic channels and capillary action to passively automate the steps of a traditional well-plate ELISA for visual read out. This work builds on prior capillary-flow devices by further simplifying operation and use of colorimetric detection. Upon adding sample, an enzyme-conjugated secondary antibody, wash steps, and substrate are sequentially delivered to test and control lines on a nitrocellulose strip generating a colorimetric response. The end user can visually detect SARS-CoV-2 antigen in 15-20 min by naked eye, or results can be quantified using a smartphone and software such as ImageJ. An analytical detection limit of 83 PFU/mL for SARS-CoV-2 was determined for virus in buffer, and 222 PFU/mL for virus spiked into nasal swabs using image analysis, similar to the LODs determined by traditional well-plate ELISA. Additionally, a visual detection limit of 100 PFU/mL was determined in contrived nasal swab samples by polling 20 untrained end-users. While the CaDI device was used for detecting clinically relevant levels of SARS-CoV-2 in this study, the CaDI device can be easily adapted to other immunoassay applications by changing the reagents and antibodies.

Rapid and Sensitive Detection of Polycyclic Aromatic Hydrocarbons in Tea Leaves Using Magnetic Approach

A rapid and efficient method using an alkyl-functionalized magnetic nanoparticles-based extraction technique combined with Ultra-High Performance Liquid Chromatography was developed for the detection of trace amounts of polycyclic aromatic hydrocarbons in tea leaves. As a popular coating for chromatographic column packing materials, C₁₈-alkyl has been demonstrated to be effective in separating polycyclic aromatic hydrocarbons. Additionally, the magnetism of the nanomaterials accelerates the extraction process while their high surface ratio enables desirable dispersity in the sample matrix. Meanwhile, the adsorbents can be washed and reused 30 times without compromising recovery, which greatly reduces the budget. The effects of various parameters were investigated and optimized, and the recoveries for five analytes were in the range of 84.8-105.4%. The RSD of intra-day and inter-day were below 11.9% and 6.8%, respectively. The limits of detection and limits of quantification ranged from 1.69-9.97 ng g^-1 and 5.12-30.21 ng g^-1, indicating satisfactory sensitivity. Thus, the proposed methodology is rapid, highly efficient, and economical, and it expands the application of magnetic cleanup approaches in complex food matrices.

Finger pump microfluidic detection system for methylparaben detection in foods

A novel assay platform consisting of a finger pump microchip (FPM) and a WiFi-based analytical detection platform is presented for measuring the concentration of methylparaben (MP) in commercial foods. In the presented approach, a low quantity (5 μL) of distilled food sample is dripped onto the FPM and undergoes a modified Fenton reaction at a temperature of 40 °C to form a green-colored complex. The MP concentration is then determined by measuring the color intensity (RGB) of the reaction complex using APP software (self-written) installed on a smartphone. The color intensity Red(R) + Green(G) value of the reaction complex is found to be linearly related (R² = 0.9944) to the MP concentration for standard samples with different MP concentrations ranging from 100 to 3000 ppm. The proposed method is used to detect the MP concentrations of 12 real-world commercial foods. The MP concentrations measurements are found to deviate by no more than 5.88% from the results obtained using a conventional benchtop method. The presented platform thus offers a feasible and low-cost alternative to existing macroscale techniques for measuring the MP concentration in commercial foods.

"Blocking-effect" detection strategy of clenbuterol by molecularly imprinted electrochemiluminescence sensor based on multiple synergistic excitation of AgNW luminophores signal with highly active BNQDs@AuNFs nanoscale co-reaction accelerator

A molecularly imprinted electrochemiluminescence sensor (MIECLS) is constructed to selectively detect clenbuterol (CLB) based on boron nitride quantum dots@gold nanoflowers/silver nanowires (BNQDs@AuNFs/AgNWs). The abundant amino and hydroxyl groups on the surface of the BNQDs generate an electrostatic self-assembly effect with the multi-tipped spatial structure of AuNFs, constituting a novel nanoscale co-reaction accelerator (NCRA) with high activity and large load capacity. An NCRA embedded in the network structure of the AgNW luminophores significantly promotes the reduction of peroxydisulfate (S₂O₈^2-) to sulfate anion radicals (SO₄^-•) through the catalysis of amino groups and boron radicals (B^•) and the electron acceleration of AuNFs while also reducing the reaction distance between SO₄^-• and AgNWs^-•, realizing the multiple synergistic amplification of the electrochemiluminescence (ECL) signal. Imprinted cavities in the molecularly imprinted polymers (MIPs) prepared by electropolymerization can generate a "blocking-effect" by recognizing CLB, realizing ECL signal quenching. Analytical results indicate that the established MIECLS detects CLB in a line concentration range of 0.5-50000 nM and detection limit of 0.00693 nM. The spiked recoveries are 85.90%-97.77%, with the relative standard deviations (RSD) under 5.1%, consistent with those of high-performance liquid chromatography (HPLC). This work demonstrates that an efficient NCRA can significantly enhance the output of the ECL signal in collaboration with the original luminophore, providing a new method to realize the ultra-detection of targeted substances by MIECLS.

Paper-based microfluidics in sweat detection: from design to application

Sweat, as a sample that includes a lot of biochemical information, is good for non-invasive monitoring. In recent years, there have been an increasing number of studies on in situ monitoring of sweat. However, there are still some challenges for the continuous analysis of samples. As a hydrophilic, easy-to-process, environmentally friendly, inexpensive and easily accessible material, paper is an ideal substrate material for making in situ sweat analysis microfluidics. This review introduces the development of paper as a sweat analysis microfluidic substrate material, focusing on the advantages of the structural characteristics of paper, trench design and equipment integration applications to expand the design and research ideas for the development of in situ sweat detection technology.

Rapid detection of three mycotoxins in animal feed materials using competitive ELISA-based origami microfluidic paper analytical device (μPAD)

We report the development of a competitive ELISA-based origami microfluidic paper-based analytical device (μPAD) for the detection of mycotoxins in animal feed material. The μPAD was patterned using the wax printing technique with the design of a testing pad in the middle and two absorption pads at the side. Anti-mycotoxin antibodies were effectively immobilized on chitosan-glutaraldehyde-modified sample reservoirs in the μPAD. The determination of zearalenone, deoxynivalenol, and T-2 toxin in corn flour was successfully achieved by performing competitive ELISA on the μPAD in 20 min. Colorimetric results were easily distinguished by the naked eye with a detection limit of 1 µg/mL for all three mycotoxins. The μPAD integrated with competitive ELISA holds potential for practical applications in the livestock industry for rapid, sensitive, and cost-effective detection of different mycotoxins in animal feed materials.

Development of a New Lab-on-Paper Microfluidics Platform Using Bi-Material Cantilever Actuators for ELISA on Paper

In this paper, we present a novel and cost-effective lab-on-paper microfluidics platform for performing ELISA autonomously, with no user intervention beyond adding the sample. The platform utilizes two Bi-Material Cantilever Valves placed in a specially designed housing. The integration of these valves in a specific channel network forms a complete fluidic logic circuit for performing ELISA on paper. The housing also incorporates an innovative reagent storage and release mechanism that minimizes variability in the volume of reagents released into the reagent pads. The platform design was optimized to minimize variance in the time of fluid wicking from the reagent pad, using a randomized design of experiment. The platform adheres to the World Health Organization's ASSURED principles. The optimized design was used to conduct an ELISA for detecting rabbit immunoglobulin G (IgG) in a buffer, with a limit of detection of 2.27 ng/mL and a limit of quantification of 8.33 ng/mL. This represents a 58% improvement over previous ELISA methods for detecting rabbit IgG in buffer using portable microfluidic technology.

Fabrication of microtiter plate on paper using 96-well plates for wax stamping

Paper-based analytical devices have prominently emerged as a group of diagnostic tools with prospective to eliminate the expensive, time-consuming, and intricate analytical methodologies. Wax printing has been a dominant technique to fabricate hydrophobic patterns on paper for fluid control, but the discontinuation of commercial solid ink printers has begun a genesis of alternate wax patterning strategies. In this study, a simple and rapid fabrication methodology for realizing a 96-well microtiter plate on paper has been developed. The method involves the use of commercially available polystyrene microplates as a stamp for wax patterning. The technique further eradicates the requirement of customized stamps and the step of heating paper substrates for creating wax barriers. Thus, wax stamped paper microplates can be used for a wide range of bioanalytical tests maneuvering reduced generation of non-biodegradable waste, minimal reagent usage, and inexpensive readout strategies. The viability of the fabricated platform has been assessed by colorimetric detection of glutathione using 3,3',5,5'-tetramethylbenzidine-H₂O₂ redox system. RGB analysis of the colorimetric response showed a linear concentration range from 0 to 90 µM (R ² = 0.989) along with a detection limit of 28.375 µM.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10404-022-02606-3.

Electromembrane extraction of clenbuterol from swine urine for monitoring illegal use in livestock

The illegal use of clenbuterol seriously endangers food safety and human health. Accurate monitoring the illegal use of clenbuterol in livestock can efficiently prevent the clenbuterol residue pork products from entering the consumer market. Thus, in this study, a simple, rapid and sensitive method for the determination of clenbuterol in swine urine was developed using electromembrane extraction combined with liquid chromatography-tandem mass spectrometry. It should be noted that the electromembrane extraction method presented many advantages of simple operation, fast mass transfer rate, good sample clean-up capability and less organic solvent consumption. The effect of important factors on the extraction efficiency of clenbuterol was investigated. Under the optimal conditions, good linearity was achieved for clenbuterol over the range of 1-1000 ng/mL (R² = 0.9996). The recoveries of clenbuterol in swine urine at three spiked levels ranged from 83.7 to 110.0% with relative standard deviation values lower than 9.7% (n = 4). Limits of detection and quantification for clenbuterol were 0.07 and 0.25 ng/mL, respectively. These results suggested that the proposed method has great potential on the extraction and determination of trace analyte in complex sample matrix for monitoring the illegal use in livestock. This article is protected by copyright. All rights reserved.

3D Paper-based milk adulteration detection device

Milk adulteration is a common problem in developing countries, and it can lead to fatal diseases in humans. Despite several studies to identify different adulterants in milk samples, the effects of multiple adulterants remain unexplored. In this work, a three-dimensional (3D) paper-based microfluidic device is designed and fabricated to simultaneously detect multiple chemical adulterants in milk. This device comprises a top cover, a bottom cover, and a middle layer composed of transportation and a detection zone. By making cuts on the middle layer's support, the device's flow path is characterised by optimum and uniform velocity. For the first time, seven adulterants (urea, detergents, soap, starch, hydrogen peroxide, sodium-hydrogen-carbonate, and salt) are detected in the milk sample simultaneously with specificity evaluation and detailed color interference analysis. Only 1-2 mL of sample volume is required to detect 7 adulterants at one time. We have used only 10 [Formula: see text]L of the reagent's volume for the colorimetric reaction and found the results within a few seconds. Observation reveals that the limit of detection (LOD) of the adulterants lies in the range between [Formula: see text] (vol./vol.) to [Formula: see text] (vol./vol.) using the colorimetric detection technique. The unknown quantity of the added adulterants is measured using the calibration curves obtained from the experiments results. The repeatability and reproducibility of the process, sensitivity, and the linear range of detection of the calibration curves and the statistical study of the color intensity data are thoroughly analysed herein. In any resource-limited setting, this simple, portable, and user-friendly 3D microfluidic device is expected to be used for testing liquid foods before consumption.

Biosensors for rapid detection of bacterial pathogens in water, food and environment

Conventional techniques (e.g., culture-based method) for bacterial detection typically require a central laboratory and well-trained technicians, which may take several hours or days. However, recent developments within various disciplines of science and engineering have led to a major paradigm shift in how microorganisms can be detected. The analytical sensors which are widely used for medical applications in the literature are being extended for rapid and on-site monitoring of the bacterial pathogens in food, water and the environment. Especially, within the low-resource settings such as low and middle-income countries, due to the advantages of low cost, rapidness and potential for field-testing, their use is indispensable for sustainable development of the regions. Within this context, this paper discusses analytical methods and biosensors which can be used to ensure food safety, water quality and environmental monitoring. In brief, most of our discussion is focused on various rapid sensors including biosensors and microfluidic chips. The analytical performances such as the sensitivity, specificity and usability of these sensors, as well as a brief comparison with the conventional techniques for bacteria detection, form the core part of the discussion. Furthermore, we provide a holistic viewpoint on how future research should focus on exploring the synergy of different sensing technologies by developing an integrated multiplexed, sensitive and accurate sensors that will enable rapid detection for food safety, water and environmental monitoring.

Microfluidic Paper-Based Analytical Devices for the Determination of Food Contaminants: Developments and Applications

Food safety is an issue that cannot be ignored at any time because of the great impact of food contaminants on people's daily life, social production, and the economy. Because of the extensive demand for high-quality food, it is necessary to develop rapid, reliable, and efficient devices for food contaminant detection. Microfluidic paper-based analytical devices (μPADs) have been applied in a variety of detection fields owing to the advantages of low-cost, ease of handling, and portability. This review systematically discusses the latest progress of μPADs, including the fundamentals of fabrication as well as applications in the detection of chemical and biological hazards in foods, hoping to provide suitable screening strategies for contaminants in foods and accelerating the technology transformation of μPADs from the lab into the field.

Paper-Based Fluidic Sensing Platforms for β-Adrenergic Agonist Residue Point-of-Care Testing

The illegal use of β-adrenergic agonists during livestock growth poses a threat to public health; the long-term intake of this medication can cause serious physiological side effects and even death. Therefore, rapid detection methods for β-adrenergic agonist residues on-site are required. Traditional detection methods such as liquid chromatography have limitations in terms of expensive instruments and complex operations. In contrast, paper methods are low cost, ubiquitous, and portable, which has led to them becoming the preferred detection method in recent years. Various paper-based fluidic devices have been developed to detect β-adrenergic agonist residues, including lateral flow immunoassays (LFAs) and microfluidic paper-based analytical devices (μPADs). In this review, the application of LFAs for the detection of β-agonists is summarized comprehensively, focusing on the latest advances in novel labeling and detection strategies. The use of μPADs as an analytical platform has attracted interest over the past decade due to their unique advantages and application for detecting β-adrenergic agonists, which are introduced here. Vertical flow immunoassays are also discussed for their shorter assay time and stronger multiplexing capabilities compared with LFAs. Furthermore, the development direction and prospects for the commercialization of paper-based devices are considered, shedding light on the development of point-of-care testing devices for β-adrenergic agonist residue detection.

Paper-based microfluidic devices for food adulterants: Cost-effective technological monitoring systems

Analytical sciences have witnessed emergent techniques for efficient clinical and industrial food adulterants detection. In this review, the contributions made by the paper-based devices are highlighted for efficient and rapid detection of food adulterants and additives, which is the need of the hour and how different categories of techniques have been developed in the past decade for upgrading the performance for point-of-care testing. A simple strategy with an arrangement for detecting specific adulterants followed by the addition of samples to obtain well-defined qualitative or quantitative signals for confirming the presence of target species. The paper-based microfluidics-based technology advances and prospects for food adulterant detection are discussed given the high-demand from the food sectors and serve as a valued technology for food researchers working in interdisciplinary technological frontiers.

G-quadruplex based biosensors for the detection of food contaminants

G-quadruplex (G4) is a very interesting DNA structure, commonly associated with cancer and its treatment. With flexible binding ability, G4 has been extended as a significant component in biosensors. On account of its simple operation, high sensitivity and low cost, G4-based biosensors have attracted considerable interest for the detection of food contaminants. In this review, research published in recent 5 years is collated from a principle perspective, that is target recognition and signal transduction. Contaminants with G4 binding capacity are illustrated, emerging G4-based biosensors including colorimetric, electrochemical and fluorescent sensors are also elaborated. The current review indicates that G4 has provided an efficient and effective solution for the rapid detection of food contaminants. A distinctive feature of G4 as recognition unit is the simple composition, but the selectivity is still unsatisfactory. As signal reporter, G4/hemin DNAzyme has not only achieved amplified signals, but also enabled visualized detection, which offers great potential for on-site measurement. With improved selectivity and visualized signal, the combination of aptamer and G4 seems to be an ideal strategy. This promising combination should be developed for the real-time monitor of multiple contaminants in food matrix.

Ultra-Sensitive, Rapid and On-Site Sensing Harmful Ingredients Used in Aquaculture with Magnetic Fluid SERS

The integration of surface-enhanced Raman scattering (SERS) spectroscopy with magnetic fluid provides significant utility in point-of-care (POC) testing applications. Bifunctional magnetic-plasmonic composites have been widely employed as SERS substrates. In this study, a simple and cost-effective approach was developed to synthesize magnetic-plasmonic SERS substrates by decorating silver nanoparticles onto magnetic Fe₃O₄ nanoparticles (AgMNPs), which function both as SERS-active substrates and magnetic fluid particles. The strong magnetic responsivity from AgMNPs can isolate, concentrate, and detect target analytes from the irregular surface of fish skin rapidly. We fabricate a microfluid chip with three sample reservoirs that confine AgMNPs into ever smaller volumes under an applied magnetic field, which enhances the SERS signal and improves the detection limit by two orders of magnitude. The magnetic fluid POC sensor successfully detected malachite green from fish with excellent selectivity and high sensitivity down to the picomolar level. This work achieves a label-free, non-destructive optical sensing approach with promising potential for the detection of various harmful ingredients in food or the environment.

Sensitive and Selective Detection of Clenbuterol in Meat Samples by a Graphene Quantum Dot Fluorescent Probe Based on Cationic-Etherified Starch

The use of clenbuterol (CLB) in large quantities in feedstuffs worldwide is illegal and potentially dangerous for human health. In this study, we directly prepared nitrogen-doped graphene quantum dots (N-GQDs) by a one-step method using cationic-etherified starch as raw material without pollution, which has the advantages of simple, green, and rapid synthesis of N-GQDs and high doping efficiency of nitrogen elements, compared with the traditional nitrogen doping method of reacting nitrogen source raw material with quantum dots. The N-GQDs synthesized by cationic etherification starch with different substitution degrees (DSs) exhibit good blue-green photoluminescence, good fluorescence stability, and water solubility. By comparing the fluorescence emission intensity of the two methods, the N-GQDs prepared by this method have higher fluorescence emission intensity and good fluorescence stability. Based on the static quenching mechanism between CLB and N-GQDs, a fluorescent probe was designed to detect CLB, which exhibited a wide linear range in the concentration range of 5 × 10⁻¹⁰~5 × 10⁻⁷ M (R² = 0.9879) with a limit of detection (LOD) of 2.083 × 10⁻¹³ M. More excitingly, the N-GQDs fluorescent probe exhibited a satisfactory high selectivity. Meanwhile, it can be used for the detection of CLB in chicken and beef, and good recoveries were obtained. In summary, the strategic approach in this paper has potential applications in the detection of risky substances in the field of food safety.

An origami paper-based analytical device for rapid detection of testosterone in healthcare food

An integrated origami paper-based analytical device (oPAD) based on competitive enzyme-linked immunosorbent assay (ELISA) was developed for testosterone (TES) detection. In this design, a positive correlation between the signals and analytes was observed due to the connection of the reaction zone and signal readout zone by a "detachable bridge". The device displayed rapid (35 min), sensitive (LOD: 1 μg L^-1) and highly selective characteristics for TES detection. In addition, complex matrices in healthcare food such as oral solutions and tablets showed a negligible effect on the accuracy of this assay (recovery: 95.4-109.1% and RSD < 6%), demonstrating its potential for hazardous chemical testing in real samples.

Tuning the Structure, Conductivity, and Wettability of Laser-Induced Graphene for Multiplexed Open Microfluidic Environmental Biosensing and Energy Storage Devices

The integration of microfluidics and electrochemical cells is at the forefront of emerging sensors and energy systems; however, a fabrication scheme that can create both the microfluidics and electrochemical cells in a scalable fashion is still lacking. We present a one-step, mask-free process to create, pattern, and tune laser-induced graphene (LIG) with a ubiquitous CO₂ laser. The laser parameters are adjusted to create LIG with different electrical conductivity, surface morphology, and surface wettability without the need for postchemical modification. Such definitive control over material properties enables the creation of LIG-based integrated open microfluidics and electrochemical sensors that are capable of dividing a single water sample along four multifurcating paths to three ion selective electrodes (ISEs) for potassium (K⁺), nitrate (NO₃^-), and ammonium (NH₄⁺) monitoring and to an enzymatic pesticide sensor for organophosphate pesticide (parathion) monitoring. The ISEs displayed near-Nernstian sensitivities and low limits of detection (LODs) (10^-5.01 M, 10^-5.07 M, and 10^-4.89 M for the K⁺, NO₃^-, and NH₄⁺ ISEs, respectively) while the pesticide sensor exhibited the lowest LOD (15.4 pM) for an electrochemical parathion sensor to date. LIG was also specifically patterned and tuned to create a high-performance electrochemical micro supercapacitor (MSC) capable of improving the power density by 2 orders of magnitude compared to a Li-based thin-film battery and the energy density by 3 orders of magnitude compared to a commercial electrolytic capacitor. Hence, this tunable fabrication approach to LIG is expected to enable a wide range of real-time, point-of-use health and environmental sensors as well as energy storage/harvesting modules.

Fluorescent sensing platform based on green luminescence carbon dots and AuNPs for clenbuterol detection in pork liver

In this paper, water-soluble green fluorescent carbon dots (G-CDs) were prepared using p-phenylenediamine and glutathione (GSH) as the precursors. The G-CDs exhibit excellent optical properties, and the maximum emission wavelength is located at 522 nm (under 410 nm excitation), which greatly overlaps with the absorption spectrum of AuNPs. Consequently, an effective “off–on” fluorescent sensing platform involved in G-CDs and AuNPs for detection of clenbuterol (CLB) was constructed. The fluorescence of G-CDs was strongly quenched by AuNPs due to the inner filter effect (IFE). As CLB was introduced, the quenched fluorescence intensity was recovered due to the specific interaction between the AuNPs and CLB. The recovered fluorescence intensity is linear to CLB concentration in the range of 13–270 ng mL⁻¹ with a low detection limit of 3.75 ng mL⁻¹. The prepared sensor has been successfully applied for CLB detection in pork liver and could be utilized in food analysis.

Carbon dots (G-CDs) with bright green fluorescence are synthesized by hydrothermal treatment of p-phenylenediamine and glutathione. Employing the G-CDs and AuNPs as sensing platform, a simple fluorescence sensor to detect clenbuterol was established.

A Membrane-Modulated Centrifugal Microdevice for Enzyme-Linked Immunosorbent Assay-Based Detection of Illicit and Misused Drugs

Increased opioid use and misuse have imposed large analytical demands across clinical and forensic sectors. Due to the absence of affordable, accurate, and simple on-site tests (e.g., point of interdiction and bedside), analysis is primarily conducted in centralized laboratories via time-consuming, labor-intensive methods. Many healthcare facilities do not have such analytical capabilities and must send samples to commercial laboratories, increasing turnaround time and care costs, as well as delaying public health warnings regarding the emergence of specific substances. Enzyme-linked immunosorbent assays (ELISAs) are used ubiquitously, despite lengthy workflows that require substantial manual intervention. Faster, reliable analytics are desperately needed to mitigate the mortality and morbidity associated with the current substance use epidemic. We describe one such alternative─a portable centrifugal microfluidic ELISA system that supplants repetitive pipetting with rotationally controlled fluidics. Embedded cellulosic membranes act as microvalves, permitting flow only when centrifugally generated hydraulic pressure exceeds their liquid entry pressure. These features enable stepwise reagent introduction, incubation, and removal simply by tuning rotational frequency. We demonstrate the success of this platform through sensitive, specific colorimetric detection of opiates, a subclass of opioids naturally derived from the opium poppy. Objective image analysis eliminated subjectivity in human color perception and permitted reliable detection of opiates in buffer and artificial urine at the ng/μL range. Opiates were clearly differentiated from other drug classes without interference from common adulterants known to cause false positive results in current colorimetric field tests. Eight samples were simultaneously analyzed in under 1 h, a marked reduction from the traditional multiday timeline. This approach could permit rapid, automatable ELISA-based drug detection outside of traditional laboratories by nontechnical personnel.