Rapid Bacteria Detection at Low Concentrations Using Sequential Immunomagnetic Separation and Paper-Based Isotachophoresis

Carbon dots-based fluorescent probe for detection of foodborne pathogens and its potential with microfluidics

Concern about food safety triggers demand on rapid, accurate and on-site detection of foodborne pathogens. Among various fluorescent probes for detection, carbon dots (CDs) prepared by carbonization of carbon-rich raw materials show extraordinary performance for their excellent and tailorable photoluminescence property, as well as their facilely gained specificity by surface customization and modification. CDs-based fluorescent probes play a crucial role in many pathogenic bacteria sensing systems. In addition, microfluidic technology with characteristics of portability and functional integration is expected to combine with CDs-based fluorescent probes for point-of-care testing (POCT), which can further enhance the detection property of CDs-based fluorescent probes. Here, this paper reviews CDs-based bacterial detection methods and systems, including the structural modulation of fluorescent probes and pathogenic bacteria detection mechanisms, and describes the potential of combining CDs with microfluidic technology, providing reference for the development of novel rapid detection technology for pathogenic bacteria in food.

Bioluminescence assay for rapid detection of live Staphylococcus aureus based on the enrichment of egg yolk antibody modified magnetic metal organic framework immunobeads

Specific and rapid detection of live Staphylococcus aureus (S.A) in environmental and food samples is critically important for protecting human health. In order to fulfill this purpose, two kinds of novel egg yolk antibody (IgY) immobilized immunomagnetic beads (IMBs; mSiO2-IgY and mMOF-IgY), with core-shell mSiO2 and mMOF as substrate, were prepared for selectively enriching S.A from samples. Furthermore, the IMBs with captured S.A were collected and re-dissolved in 0.5 mL PBS. After that, a cotton swab coated with sodium dodecylsulfate (SDS) was put in the solution to lyse S.A cells and emit ATP bioluminescence of the luciferin/luciferase system. Finally, a portable bioluminescence detector was used for quantification of ATP corresponding to S.A concentration. The results demonstrated that mMOF-IgY can enrich more S.A than mSiO2-IgY and emit a stronger signal. The reasons may be due to the higher immobilization amount of IgY on the IMBs. Under optimal conditions, the calibration line of S.A concentration was 10-105 CFU mL-1 by mMOF-IgY within 30 min. The low detection limit of S.A was 3 CFU mL-1. The results demonstrated that the assay takes much shorter time than plate counting. Its portability and excellent detection capability are suitable for rapid monitoring of specific pathogens in foods.

A nanogap-enhanced SERS nanotag-based lateral flow assay for ultrasensitive and simultaneous monitoring of SARS-CoV-2 S and NP antigens

A lateral flow assay (LFA) strip based on dual 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB)-encoded satellite Fe3O4@Au (Mag@Au) SERS tags with nanogap is reported for  ultrasensitive and simultaneous diagnosis of two SARS-CoV-2 functional proteins. Composed of Fe3O4 core, satellite gold shell with nanogaps, and double-layer DTNB, the Mag@Au nanoparticles with an average size of 238 nm were designed as multifunctional tags to efficiently enrich the target SARS-CoV-2 protein from complex samples, significantly enhancing the SERS signal of the LFA strip and provide quantitative SERS detection of analyte on test lines. The developed dual DTNB-encoded satellite Mag@Au-based LFA allowed simultaneous quantification of spike (S) protein and nucleocapsid (NP) protein with detection limits of 23 pg mL-1 and 2 pg mL-1, respectively, lower than commercial ELISA kits and reported SERS-LFA detection system-based Au NPs and Fe3O4@3 nm Au MNPs. This magnetic SERS-LFA also showed high performance of multi-variant strain detection and further distinguished clinical samples of Omicron variant infection, demonstrating the potential of in situ detection of respiratory virus diseases.

Detection of Vibrio parahaemolyticus Based on Magnetic and Upconversion Nanoparticles Combined with Aptamers

Vibrio parahaemolyticus is a halophilic and heat-labile gram-negative bacterium and is the most prevalent foodborne bacterium in seafood. In order to develop a rapid and sensitive method for detecting the foodborne pathogenic bacterium Vibrio parahaemolyticus, an aptamer-modified magnetic nanoparticle and an aptamer-modified upconversion nanoparticle were synthesised and used as a capture probe and a signal probe, respectively. The aptamer-modified magnetic nanoparticle, V. parahaemolyticus cell, and aptamer-modified upconversion nanoparticle formed a sandwich-like complex, which was rapidly separated from a complex matrix using a magnetic force, and the bacterial concentration was determined by fluorescence intensity analysis. The results showed that the fluorescence intensity signal correlated positively with the concentration of V. parahaemolyticus in the range of 3.2 × 102 to 3.2 × 105 CFU/mL, with a linear equation of y = 296.40x - 217.67 and a correlation coefficient of R2 = 0.9610. The detection limit of the developed method was 4.4 CFU/mL. There was no cross-reactivity with other tested foodborne pathogens. This method is highly specific and sensitive for the detection of V. parahaemolyticus, and can achieve the qualitative detection of this bacterium in a complex matrix.

The colorful world of sulfonephthaleins: Current applications in analytical chemistry for "old but gold" molecules

Sulfonephthaleins represent one of the most common and widely employed reactive dyes in analytical chemistry, thanks to their stability, low-cost, well-visible colors, reactivity and possibilities of chemical modification. Despite being first proposed in 1916, nowadays, these molecules play a fundamental role in biological and medical applications, environmental analyses, food quality monitoring and other fields, with a particular focus on low-cost and disposable devices or methods for practical applications. Since up to our knowledge, no reviews or book chapters focused explicitly on sulfonephthaleins have ever been published, in this review, we will briefly describe sulfonephthaleins history, their acid-base properties will be discussed, and the most recent applications in different fields will be presented, focusing on the last ten years literature (2014-2023). Finally, safety and environmental issues will be briefly discussed, despite being quite controversial.

Multifunctional Nanoprobe-Amplified Enzyme-Linked Immunosorbent Assay on Capillary: A Universal Platform for Simple, Rapid, and Ultrasensitive Dual-Mode Pathogen Detection

Although the traditional enzyme-linked immunosorbent assay (ELISA) has been widely applied in pathogen detection and clinical diagnostics, it always suffers from complex procedures, a long incubation time, unsatisfying sensitivity, and a single signal readout. Here, we developed a simple, rapid, and ultrasensitive platform for dual-mode pathogen detection based on a multifunctional nanoprobe integrated with a capillary ELISA (CLISA) platform. The novel capture antibodies-modified capillaries can act as a swab to combine in situ trace sampling and detection procedures, eliminating the dissociation between sampling and detection in traditional ELISA assays. With excellent photothermal and peroxidase-like activity, the Fe₃O₄@MoS₂ nanoprobe with a unique p-n heterojunction was chosen as an enzyme substitute and amplified signal tag to label the detection antibody for further sandwich immune sensing. As the analyte concentration increased, the Fe₃O₄@MoS₂ probe could generate dual-mode signals, including remarkable color changes from the chromogenic substrate oxidation as well as photothermal enhancement. Moreover, to avoid false negative results, the excellent magnetic capability of the Fe₃O₄@MoS₂ probe can be used to pre-enrich the trace analytes, amplifying the detection signal and enhancing the immunoassay's sensitivity. Under optimal conditions, specific and rapid detection of SARS-CoV-2 has been realized successfully based on this integrated nanoprobe-enhanced CLISA platform. The detection limits were 5.41 pg·mL^-1 for the photothermal assay and 150 pg·mL^-1 for the visual colorimetric assay. More importantly, the simple, affordable, and portable platform can also be expanded to rapidly detect other targets such as Staphylococcus aureus and Salmonella typhimurium in practical samples, making it a universal and attractive tool for multiple pathogen analysis and clinical testing in the post COVID-19 era.

Ag+-gated peroxidase activity of gold nanoparticles for sensitive detection of Escherichia coli

Escherichia coli (E. coli) is one of the most ubiquitous foodborne pathogens that can cause infections and threaten human health. Herein, a colorimetric method for sensitive detection of E. coli was established by using enzyme-nanozyme cascade reaction for signal amplification. Gold nanoparticles (AuNPs) are well-known nanozymes due to their high peroxidase-like activity. When the dense cetyltrimethylammonium bromide (CTAB) membrane on the surfaces of AuNPs kept the substrate away from AuNPs, the peroxidase activity of AuNPs was inhibited. However, the CTAB membrane could be disrupted by Ag⁺, resulting in enhanced peroxidase activity of AuNPs. When E. coli was present, the enzyme-nanozyme cascade reaction was initiated. The substrate p-aminophenyl β-D-galactopyranoside (PAPG) was hydrolyzed to the reductive p-aminophenol (PAP) by beta-galactosidase (β-gal) in E. coli, reducing Ag⁺ to Ag. Consequently, CTAB-AuNPs remained weak peroxidase activity and could not catalyze the H₂O₂-mediated oxidation of TMB. As the amount of E. coli increased, the absorbance of TMB decreased along with a color change from deep blue to pink. The absorbance intensity displayed a linear dependence on E. coli from 1.0 × 10² to 1.0 × 10⁹ CFU mL^-1. Therefore, the proposed method holds good prospects in foodborne pathogenic bacteria detection.

Microfluidic paper and thread-based separations: Chromatography and electrophoresis

Paper and thread are widely used as the substrates for fabricating low-cost, disposable, and portable microfluidic analytical devices used in clinical, environmental, and food safety monitoring. Concerning separation methods including chromatography and electrophoresis, these substrates provide unique platforms for developing portable devices. This review focuses on summarizing recent research on the miniaturization of the separation techniques using paper and thread. Preconcentration, purification, desalination, and separation of various analytes are achievable using electrophoresis and chromatography methods integrated with modified or unmodified paper/thread wicking channels. A variety of 2D and 3D designs of paper/thread platforms for zone electrophoresis, capillary electrophoresis, and modified/unmodified chromatography are discussed with emphasis on their limitation and improvements. The current progress in the signal amplification strategies such as isoelectric focusing, isotachophoresis, ion concentration polarization, isoelectric focusing, and stacking methods in paper-based devices are reviewed. Different strategies for chromatographic separations based on paper/thread will be explained. The separation of target species from complex samples and their determination by integration with other analytical methods like spectroscopy and electrochemistry are well-listed. Furthermore, the innovations for plasma and cell separation from blood as an important human biofluid are presented, and the related paper/thread modification methods are explored.

Paper-based analytical device coupled with Bi-MOF: Electric field amplification and fluorescence sensing of glyphosate

Glyphosate, a potent herbicide wildly used in the world, involves potential hazards to human health by accumulating in the food chain. Due to its absence of chromophores and fluorophores, the rapid visual detection of glyphosate has always been difficult. Herein, a paper-based geometric field amplification device visualized by the amino-functionalized bismuth-based metal-organic framework (NH₂-Bi-MOF) was constructed for sensitive fluorescence determination of glyphosate. Fluorescence of the synthesized NH₂-Bi-MOF was immediately enhanced by interaction with glyphosate. The field amplification of glyphosate was implemented by coordinating the electric field and the electroosmotic flow, which was orchestrated by the geometric configuration of paper channel and the concentration of polyvinyl pyrrolidone, respectively. Under the optimal conditions, the developed method exhibited a linear range of 0.80-200 μmol L^-1 with about 12500-fold signal enhancement achieved by just 100 s electric field amplification. It was applied to soil and water with recoveries between 95.7% and 105.6%, holding great prospects in on-site analysis of hazardous anions for environment safety.

Paper-based sensors for bacteria detection

The detection of pathogenic bacteria is essential to prevent and treat infections and to provide food security. Current gold-standard detection techniques, such as culture-based assays and polymerase chain reaction, are time-consuming and require centralized laboratories. Therefore, efforts have focused on developing point-of-care devices that are fast, cheap, portable and do not require specialized training. Paper-based analytical devices meet these criteria and are particularly suitable to deployment in low-resource settings. In this Review, we highlight paper-based analytical devices with substantial point-of-care applicability for bacteria detection and discuss challenges and opportunities for future development.

Magnetic microbead enzyme-linked immunoassay based on phage encoded protein RBP 41-mediated for rapid and sensitive detection of Salmonella in food matrices

Rapid and sensitive quantitative detection methods are required to monitor and detect Salmonella throughout the food supply chain and early prevention of foodborne disease outbreaks. In this study, a magnetic microbead enzyme-linked immunoassay (MELISA) based on phage receptor binding protein was developed for rapid enrichment and detection of Salmonella in complex food matrices. RBP 41 from phage T102 acted as a species-specific recognition element for Salmonella by exploiting its strong binding capacity to Salmonella surface receptors. RBP 41-MBs were prepared by coupling recombinant RBP 41 with MBs and used to separate and enrich Salmonella cells from spiked food samples. The captured complexes were further integrated with ELISA procedures by HRP-labeled anti-Salmonella antibody for rapid and accurate detection of Salmonella. The whole method took <1.5 h and the detection limit was 10 CFU/mL. Therefore, MELISA was successfully developed for the detection of Salmonella in various spiked food samples (skim milk, lettuce, and chicken breast). The ELISA reaction process of this method was carried out on magnetic beads. It simplified the process of the traditional ELISA method and reduces the reaction time. This study expanded the use of phage-associated proteins and demonstrated the promising prospects for practical applications in the detection of foodborne pathogens.

An enzyme-activatable dual-readout probe for sensitive β-galactosidase sensing and Escherichia coli analysis

Rapid and accurate sensing of β-galactosidase (β-gal) activity is particularly critical for the early detection of many diseases and has become a topic of interest in recent years. However, most traditional probes for β-gal sensing often suffer from the disadvantages of narrow dynamic range, low reaction efficiency and are only employed with either colorimetric or fluorescence sensing. Furthermore, β-galactosidase sensing based assay for efficient detection and antibiotic resistance analysis of Escherichia coli (E.coli) is not available. Here, an enzyme-induced probe assay was reported for dual sensitive fluorescence and colorimetric measurement of β-gal activity, and was further employed for detection of Escherichia coli and their antibiotic resistance analysis. The DCM-βgal probe was virtually non-emissive in aqueous solution, while it could be activated by β-gal to produce bright emission. Under optimized conditions, DCM-βgal displayed high sensitivity, selectivity and rapid response to β-gal with a low detection limit of 1.5 × 10⁻³ U ml⁻¹. Importantly, this assay was successfully applied to sensitive detection of E. coli cells with a fast detection process within 5 h and a low detection concentration of 1 × 10³ CFU ml⁻¹. Furthermore, the enzyme-activatable assay was also successfully applied for high throughput E. coli antibiotic resistance analysis. The DCM-βgal strategy is applied for the first time on the detection of E. coli cells and their antibiotic resistance analysis. It is provided with the advantages of high selectively, a simple operation, low cost and rapid detection. The detection platform can also be extended to analyze the level of β-gal in other types of cells or biological samples. Overall, the simple, effective and dual-readout assay holds promise for efficient sensing of β-gal activity and provides a potential tool for E. coli detection and their antibiotic resistance analysis.

An automatic centrifugal system for rapid detection of bacteria based on immunomagnetic separation and recombinase aided amplification

This study reported an automatic centrifugal system for rapid quantification of foodborne pathogenic bacteria based on immunomagnetic separation (IMS) for target bacteria enrichment and recombinase aided amplification (RAA) for nucleic acid detection. First, target bacteria were captured by immune magnetic nanoparticles (MNPs) to form magnetic bacteria, which were purified and enriched by magnetic separation. Then, nucleic acid extraction buffer was used to extract genomic DNA of magnetic bacteria and dissolve lyophilized RAA reagent. Finally, isothermal amplification and fluorescent detection were conducted for bacteria quantification. Bacteria magnetic separation, nucleic acid extraction and fluorescent RAA detection were elaborately achieved in a centrifugal disc with unique functional chambers and multistage siphon channels. A supporting device was developed to automatically and successively perform the programmed centrifugal protocol, including temperature control for isothermal amplification and fluorescence detection for real-time RAA analysis. Under optimal conditions, this centrifugal system enabled Salmonella detection as low as 10 CFU mL^-1 in spiked chicken samples in 1 h with average recovery of 105.6% and average standard deviation of 8.4%. It has been demonstrated as an alternative for rapid detection of Salmonella.

Recent progress in analytical capillary isotachophoresis (2018 - March 2022)

This review brings a survey of papers on analytical capillary and microchip isotachophoresis published since 2018 until the first quarter of 2022. Theoretical papers extending fundamental knowledge include those on computer simulations that remain an important research tool useful in the design of electrolyte systems. Many papers are focused on instrumental aspects where new media including microfluidic devices and their hyphenation to various detection techniques bring remarkable results. Papers reporting analytical applications demonstrate the potential of contemporary analytical isotachophoresis. Although it is not being used on a mass scale, its special features are attracting continued interest resulting in applications of isotachophoresis both as a stand-alone analytical method and as a part of multidimensional separation techniques.

Golf-shaped Bi2Se3 microparticles based-immunochromatographic strip for ultrasensitive detection of Acetamiprid

Rapid and sensitive detection of pesticide is of significance to the field of food safety and human health, but it is still challenging due to interferents from complex food matrices. Herein, a superb golf-shaped Bi₂Se₃ microparticles-based immunochromatographic strip (BS MPs-ICS) was constructed for ultrasensitive detection of acetamiprid (ATM). The novel immune signal tag demonstrated outstanding luminance, excellent biocompatibility, and high affinity with ATM (affinity constant was 3.874 ×10⁷ M^-1), which not only possessed a preeminent labeling efficiency but also significantly improved detection sensitivity. After optimization, the limit of detection (LOD) of the BS MPs-ICS was 8.780 pg/mL with an excellent linear relationship at the range of 0.010-6.000 ng/mL, which was approximately 62-fold lower than that of conventional gold nanoparticles-ICS (0.545 ng/mL), The BS MPs-ICS biosensor was well applied in apple and tomato samples with satisfactory recoveries of 83.823-99.223% (relative standard deviation < 1.739%). Therefore, the BS MPs-ICS could serve as a promising candidate for ATM detection in complicated samples and develop a new method in real-time monitoring.

Biomineralization-inspired magnetic nanoflowers for sensitive miRNA detection based on exonuclease-assisted target recycling amplification

Biomineralization-inspired magnetic hybrid nanoflowers were prepared facilely, and capture probes were easily immobilized on the obtained nanoflowers without tedious processing. Based on the magnetic hybrid nanoflowers and exonuclease-assisted target recycling amplification, a fluorescence miRNA sensor was fabricated. The presence of target miRNA leads to the formation of the double-strand structure, which would then be selectively digested by the exonuclease and increase fluorescence intensity. The target miRNA can be released for recycling and signal amplification. Under optimized reaction conditions, the hybrid nanoflower-based miRNA sensor had a broad detection range from 0.001 nM to 100 nM and a limit of detection of 0.23 pM (S/N = 3). The sensitive detection of miRNA in serum was also achieved with recoveries from 94.3% to 116.1%. This work provides a new insight into the fabrication of bioconjugated materials and shows great potential in miRNA sensing.

Advances in bacterial concentration methods and their integration in portable detection platforms: A review

Early detection and identification of microbial contaminants is crucial in many sectors, including clinical diagnostics, food quality control and environmental monitoring. Biosensors have recently gained attention among other bacterial detection technologies due to their simplicity, rapid response, selectivity, and integration/miniaturization potential in portable microfluidic platforms. However, biosensors are limited to the analysis of small sample volumes, and pre-concentration steps are necessary to reach the low sensitivity levels of few bacteria per mL required in the analysis of real clinical, industrial or environmental samples. Many platforms already exist where bacterial detection and separation/accumulation systems are integrated in a single platform, but they have not been compiled and critically analysed. This review reports on most recent advances in bacterial concentration/detection platforms with emphasis on the concentration strategy. Systems based on five concentration strategies, i.e. centrifugation, filtration, magnetic separation, electric separation or acoustophoresis, are here presented and compared in terms of processed sample volume, concentration efficiency, concentration time, ability to work with different types of samples, and integration potential, among others. The critical evaluation presented in the review is envision to facilitate the development of future platforms for fast, sensitive and in situ bacterial detection in real sample.

Mag-spinner: a next-generation Facile, Affordable, Simple, and porTable (FAST) magnetic separation system

Mag-spinner, a system in which magnets are combined with a spinner system, is a new type of magnetic separation system for the preprocessing of biological and medical samples. Interference by undesired components restricts the detection accuracy and efficiency. Thus, the development of appropriate separation techniques is required for better detection of the desired targets, to enrich the target analytes and remove the undesired components. The strong response of iron oxide nanoclusters can successfully capture the targets quickly and with high efficiency. As a result, cancer cells can be effectively separated from blood using the developed mag-spinner system. Indeed, this system satisfies the requirements for desirable separation systems, namely (i) fast sorting rates, (ii) high separation efficiency, (iii) the ability to process native biological fluids, (iv) simple operating procedures, (v) low cost, (vi) operational convenience, and (vii) portability. Therefore, this system is widely applicable to sample preparation without limitations on place, cost, and equipment.

Online and offline preconcentration techniques on paper-based analytical devices for ultrasensitive chemical and biochemical analysis: A review

Microfluidic paper-based analytical devices (μPADs) have attracted much attention over the past decade. They embody many advantages, such as abundance, portability, cost-effectiveness, and ease of fabrication, making them superior for clinical diagnostics, environmental monitoring, and food safety assurance. Despite these advantages, μPADs lack the high sensitivity to detect many analytes at trace levels than other commercial analytical instruments such as mass spectrometry. Therefore, a preconcentration step is required to enhance their sensitivity. This review focuses on the techniques used to separate and preconcentrate the analytes onto the μPADs, such as ion concentration polarization, isotachophoresis, and field amplification sample stacking. Other separations and preconcentration techniques, including liquid-solid and liquid-liquid extractions coupled with μPADs, are also reviewed and discussed. In addition, the fabrication methods, advantages, disadvantages, and the performance evaluation of the μPADs concerning their precision and accuracy were highlighted and critically assessed. Finally, the challenges and future perspectives have been discussed.

Recognition elements based on the molecular biological techniques for detecting pesticides in food: A review

Excessive use of pesticides can cause contamination of the environment and agricultural products that are directly threatening human life and health. Therefore, in the process of food safety supervision, it is crucial to conduct sensitive and rapid detection of pesticide residues. The recognition element is the vital component of sensors and methods for fast testing pesticide residues in food. Improper recognition elements may lead to defects of testing methods, such as poor stability, low sensitivity, high economic costs, and waste of time. We can use the molecular biological technique to address these challenges as a good strategy for recognition element production and modification. Herein, we review the molecular biological methods of five specific recognition elements, including aptamers, genetic engineering antibodies, DNAzymes, genetically engineered enzymes, and whole-cell-based biosensors. In addition, the application of these identification elements combined with biosensor and immunoassay methods in actual detection was also discussed. The purpose of this review was to provide a valuable reference for further development of rapid detection methods for pesticide residues.

Nanoparticle-based amplification for sensitive detection of β-galactosidase activity in fruits

Development of fast and sensitive assays for enzyme activity detection has received a great deal of attention because of the wide spread applications in measurements of numerous clinical, food and environmental processes. Herein, a novel amplification approach to enhance the sensitivity of colorimetric assays for detection of β-galactosidase (β-Gal) activity is proposed. β-Gal detection is important in biomedical applications and in food industry, where it is associated with the ripening process of fruits. The method is based on the use of multivalent cerium oxide nanoparticles (CeNPs) which catalyze the oxidation of 4-aminophenol (4-AP) produced in the hydrolysis process of the 4-aminophenyl-β-d-galactopyranoside substrate (4-APG) by β-Gal, thus enhancing detection sensitivity of β-Gal in the visible range. The developed assay is highly sensitive and easy to use. Using the optimized procedure, a limit of detection of 0.06 mU/mL was obtained with a linearity range up to 2.0 mU/mL. The feasibility of the method was demonstrated for detection of β-Gal activity in fruits and the results were compared with the conventional assay, providing over a 30-fold amplification as compared to a commercially available β-Gal protocol. The advantage of the presented assay is its biocatalytic event amplified by a secondary reaction, which enables much more sensitive detection of the enzymatic product. The sensing platform can be applied broadly to a variety of applications that rely on β-Gal activity measurements.

Fully integrated sampler and dilutor in an electrochemical paper-based device for glucose sensing

An electroanalytical platform capable to take and dilute the sample has been designed in order to fully integrate the different steps of the analytical process in only one device. The concept is based on the addition of glass-fiber pads for sampling and diluting to an electrochemical cell combining a paper-based working electrode with low-cost connector headers as counter and reference electrodes. In order to demonstrate the feasibility of this all-in-one platform for biosensing applications, an enzymatic sensor for glucose determination (requiring a potential as low as −0.1 V vs. gold-plated wire by using ferrocyanide as mediator) was developed. Real food samples, such as cola beverages and orange juice, have been analyzed with the bioelectroanalytical lab-on-paper platform. As a proof-of-concept, and trying to go further in the integration of steps, sucrose was successfully detected by depositing invertase in the sampling strip. This enzyme hydrolyzes sucrose into fructose and glucose, which was determined using the enzymatic biosensor. This approach opens the pathway for the development of devices applying the lab-on-paper concept, saving costs and time, and making possible to perform decentralized analysis with high accuracy.

Recent Advances in Nanomaterials Development for Nanomedicine and Cancer

Cancer is considered one of the leading causes of death, with a growing number of cases worldwide. However, the early diagnosis and efficient therapy of cancer have remained a critical challenge. The emergence of nanomedicine has opened up a promising window to address the drawbacks of cancer detection and treatment. A wide range of engineered nanomaterials and nanoplatforms with different shapes, sizes, and composition has been developed for various biomedical applications. Nanomaterials have been increasingly used in various applications in bioimaging, diagnosis, and therapy of cancers. Recently, numerous multifunctional and smart nanoparticles with the ability of simultaneous diagnosis and targeted cancer therapy have been reported. The multidisciplinary attempts led to the development of several exciting clinically approved nanotherapeutics. The nanobased materials and devices have also been used extensively to develop point-of-care and highly sensitive methods of cancer detection. In this review article, the most significant achievements and latest advances in the nanomaterials development for cancer nanomedicine are critically discussed. In addition, the future perspectives of this field are evaluated.

Lab-on-Paper Devices for Diagnosis of Human Diseases Using Urine Samples-A Review

In recent years, microfluidic lab-on-paper devices have emerged as a rapid and low-cost alternative to traditional laboratory tests. Additionally, they were widely considered as a promising solution for point-of-care testing (POCT) at home or regions that lack medical infrastructure and resources. This review describes important advances in microfluidic lab-on-paper diagnostics for human health monitoring and disease diagnosis over the past five years. The review commenced by explaining the choice of paper, fabrication methods, and detection techniques to realize microfluidic lab-on-paper devices. Then, the sample pretreatment procedure used to improve the detection performance of lab-on-paper devices was introduced. Furthermore, an in-depth review of lab-on-paper devices for disease measurement based on an analysis of urine samples was presented. The review concludes with the potential challenges that the future development of commercial microfluidic lab-on-paper platforms for human disease detection would face.

Recent Developments and Applications of Microfluidic Paper-Based Analytical Devices for the Detection of Biological and Chemical Hazards in Foods: A Critical Review

Nowadays, food safety has become a major concern for the sustainability of global public health. Through the production and distribution steps, food can be contaminated by either chemical hazards or pathogens, and the determination of these plays a critical role in the processes of ensuring food safety. Therefore, the development of analytical tools that can provide rapid screening of these hazards is highly necessary. Microfluidic paper-based analytical devices (µPADs) have advanced significantly in recent years as they are rapid and low-cost analytical screening tools for testing contaminated food products. This review focuses on recent developments of µPADs for various applications in the food safety field. A description of the fabrication of selected papers is briefly discussed, and evaluation of the μPADs' performance with regard to their precision and accuracy as well as their limits of detection is critically assessed. The advantages and disadvantages of these devices are highlighted.

Visual and quantitative detection of E. coli O157:H7 by coupling immunomagnetic separation and quantum dot-based paper strip

Simple and visual quantitative detection of foodborne pathogens can effectively reduce the outbreaks of foodborne diseases. Herein, we developed a simple and sensitive quantum dot (QD)-based paper device for visual and quantitative detection of Escherichia coli (E. coli) O157:H7 based on immunomagnetic separation and nanoparticle dissolution-triggered signal amplification. In this study, E. coli O157:H7 was magnetically separated and labeled with silver nanoparticles (AgNPs), and the AgNP labels can be converted into millions of Ag ions, which subsequently quench the fluorescence of QDs in the paper strip, which along with the readout can be visualized and quantified by the change in length of fluorescent quenched band. Owing to the high capture efficiency and effective signal amplification, as low as 500 cfu mL^-1 of E. coli O157:H7 could be easily detected by naked eyes. Furthermore, this novel platform was successfully applied to detect E. coli O157:H7 in spiked milk samples with good accuracy, indicating its potential in the detection of foodborne pathogens in real samples.

Fast detection of E. coli with a novel fluorescent biosensor based on a FRET system between UCNPs and GO@Fe3O4 in urine specimens

Biosensors based on nanomaterials are becoming a research hotspot for the rapid detection of pathogenic bacteria. Herein, a "turn-on" fluorescent biosensor based on a FRET system was constructed for the fast detection of a representative pathogenic microorganism, namely, E. coli, which causes most urinary tract infections. This biosensor was constructed by utilizing synthesized UCNPs as fluorescent donors with stable luminescence performance in complex biological samples and GO@Fe3O4 as a receptor with both excellent adsorption ability and fluorescence quenching ability. A specific ssDNA selected as an aptamer which could recognize E. coli was immobilized on the UCNPs to form UCNP-Apt nanoprobes. The nanoprobes were adsorbed on the surface of GO@Fe3O4 through the π-stacking interactions between aptamers and GO. In the presence of E. coli, UCNP-Apt nanoprobes detached from GO@Fe3O4 due to the specific recognition of aptamers and bacteria, resulting in obvious fluorescence recovery, and the concentration of bacteria was positively correlated with the intensity of the fluorescence signal; such a "turn-on" signal output mode ensures excellent precision. In addition, the easy magnetic separation of GO@Fe3O4 simplifies the operation process, helping the sensor detect bacteria in 30 minutes with a linear range from 103 to 107 CFU mL-1 and a limit of detection of 467 CFU mL-1. Moreover, recovery test results also showed that the sensor has clinical application potential for the rapid detection of pathogenic microorganisms in complex biological samples.

Recent advances in lab-on-paper diagnostic devices using blood samples

Lab-on-paper, or microfluidic paper-based analytical devices (μPADs), use paper as a substrate material, and are patterned with a system of microchannels, reaction zones and sensing elements to perform analysis and detection. The sample transfer in such devices is performed by capillary action. As a result, external driving forces are not required, and hence the size and cost of the device are significantly reduced. Lab-on-paper devices have thus attracted significant attention for point-of-care medical diagnostic purposes in recent years, particularly in less-developed regions of the world lacking medical resources and infrastructures. This review discusses the major advances in lab-on-paper technology for blood analysis and diagnosis in the past five years. The review focuses particularly on the many clinical applications of lab-on-paper devices, including diabetes diagnosis, acute myocardial infarction (AMI) detection, kidney function diagnosis, liver function diagnosis, cholesterol and triglyceride (TG) analysis, sickle-cell disease (SCD) and phenylketonuria (PKU) analysis, virus analysis, C-reactive protein (CRP) analysis, blood ion analysis, cancer factor analysis, and drug analysis. The review commences by introducing the basic transmission principles, fabrication methods, structural characteristics, detection techniques, and sample pretreatment process of modern lab-on-paper devices. A comprehensive review of the most recent applications of lab-on-paper devices to the diagnosis of common human diseases using blood samples is then presented. The review concludes with a brief summary of the main challenges and opportunities facing the lab-on-paper technology field in the coming years.

Engineering paper-based visible light-responsive Sn-self doped domed SnO2 nanotubes for ultrasensitive photoelectrochemical sensor

Exploring novel photoactive materials with high photoelectric conversion efficiency plays a crucial role in enhancing the analytical performance of paper-based photoelectrochemical (PEC) biosensor. SnO₂, which possesses higher photostability and electron mobility, can be regarded as a promising photoactive material. Herein, paper-based one dimensional (1D) domed SnO₂ nanotubes (NTs) have been developed with the template-consumption strategy. What's more, their growth mechanism has also been proposed based on the controllable experiments. At first, the paper-based 1D ZnO nanorods (NRs) as the typical amphoteric oxide are prepared and serve as the sacrifice templates which can be etched by the generated alkaline environment during the formation of SnO₂. At a certain stage, all the ZnO NRs can be completely etched by controlling the experimental conditions, resulting in the forming of vertically distributed hollow SnO₂ NTs. Furthermore, the Sn self-doping strategy is also proposed to suppress the recombination of charge carriers and broaden the light response range by introducing the impurity energy levels. Profiting from such doping strategy, the prominent photocurrent signal is obtained compared with pure paper-based SnO₂ NTs. Ultimately, an innovative visible light responsive paper-based Sn-doping SnO_2-x NTs are developed and employed as the photoelectrode for the PEC biosensor using the alpha fetoprotein (AFP) as the model analyte. Under the optimal conditions, the ultrasensitive AFP sensing is realized with the linear range and detection limitation of 10 pg mL^-1 to 200 ng mL^-1 and 3.84 pg mL^-1, respectively. This work provides a judiciously strategy for developing novel photoactive materials for paper-based PEC bioanalysis.

A simple magnetic-assisted microfluidic method for rapid detection and phenotypic characterization of ultralow concentrations of bacteria

Isolation and enumeration of bacteria at ultralow concentrations and antibiotic resistance profiling are of great importance for early diagnosis and treatment of bacteremia. In this work, we describe a simple, rapid, and versatile magnetic-assisted microfluidic method for rapid bacterial detection. The developed method enables magnetophoretic loading of bead-captured bacteria into the microfluidic chamber under external static and dynamic magnetic fields in 4 min. A shallow microfluidic chamber design that enables the monolayer orientation and transportation of the beads and a glass substrate with a thickness of 0.17 mm was utilized to allow high-resolution fluorescence imaging for quantitative detection. Escherichia coli (E. coli) with green fluorescent protein (GFP)-expressing gene and streptavidin-modified superparamagnetic microbeads were used as model bacteria and capturing beads, respectively. The specificity of the method was validated using Lactobacillus gasseri as a negative control group. The limit of detection and limit of quantification values were determined as 2 CFU/ml and 10 CFU/ml of E. coli, respectively. The magnetic-assisted microfluidic method is a versatile tool for the detection of ultralow concentrations of viable bacteria with the linear range of 5-5000 CFU/ml E. coli in 1 h, and providing growth curves and phenotypic characterization bead-captured E. coli in the following 5 h of incubation. Our results are promising for future rapid and sensitive antibiotic susceptibility testing of ultralow numbers of viable cells.

A universal SERS-label immunoassay for pathogen bacteria detection based on Fe3O4@Au-aptamer separation and antibody-protein A orientation recognition

Rapid, reliable and sensitive detection methods for pathogenic bacteria are strongly demanded. Herein, we proposed a magnetically assisted surface enhanced Raman scattering (SERS)-label immunoassay for the sensitive detection of bacteria by using a universal approach based on free antibody labelling and staphylococcus proteins A (PA)-SERS tags orientation recognition. The SERS biosensor consists of two functional nanomaterials: aptamer-conjugated Fe₃O₄@Au magnetic nanoparticles (MNPs) as magnetic SERS platform for pathogen enrichment and PA modified-SERS tags (Au@DTNB@PA) as a universal probe for target bacteria quantitative detection. After target bacteria enriched, free antibody was used to specific marking target bacteria and provided numerous Fc fragment, which can guide the PA-SERS tags orientation-dependent binding. With this strategy, Fe₃O₄@Au/bacteria/SERS tags sandwich immunocomplexes for most bacteria (expect several species of Staphylococcus) were easy constructed. The limits of detection (LODs) of the proposed assay were found to be 10, 10, and 25 cells/mL for three common pathogens Escherichia coli (E. coli), Listeria monocytogenes (L. mono), and Salmonella typhimurium (S. typhi), respectively, in real food samples. The universal method also exhibits the advantages of rapid, robust, and easy to operate, suggesting its great potential for food safety monitoring and infectious diseases diagnosis.

Faster Detection of Staphylococcus aureus in Milk and Milk Powder by Flow Cytometry

A flow cytometry (FCM)-based method was developed for the faster detection of Staphylococcus aureus in milk and milk powder. Viable S. aureus cells were recognized by highly selective, fluorescently labeled antibodies and Propidium Iodide, and then analyzed by FCM. Using a 5-h pre-enrichment period, the method could detect low numbers of S. aureus cells in 6 h, with a limit of detection of 7.50 cells/mL in milk and 8.30 cells/g in milk powder. The established method was compared with the plate-based method using 75 ultra-high-temperature-treated milk samples, 25 pasteurized milk samples, 66 raw milk samples, and 123 milk powder samples. The two methods yielded similar results for the detection of the pathogen in all sample types. The FCM-based method allows effective and faster monitoring of S. aureus contamination and can be applied to the rapid detection of microorganisms in milk and dairy products.

Precise electroosmotic flow measurements on paper substrates

A novel method for electroosmotic flow (EOF) measurement on paper substrates is presented; it is based on dynamic mass measurements by simply using an analytical balance. This technique provides a more reliable alternative to other EOF measurement methods on porous media. The proposed method is used to increase the amount and quality of the available information about physical parameters that characterize fluid flow on microfluidic paper-based analytical devices (μPADs). Measurements were performed on some of the most frequently used materials for μPADs, i.e., Whatman #1 , S&S, and Muntktell 00A filter paper. Obtained experimental results are consistent with the few previously reported data, either experimental or numerical, characterizing EOF in paper substrates. Moreover, a thorough analysis is presented for the quantification of the different effects that affect the measurements such as Joule effect and evaporation. Experimental results enabled, for the first time, to establish well-defined electroosmotic characteristics for the three substrates in terms of the magnitude of EOF as funtion of pH, enabling researchers to make a rational choice of the substrate depending on the electrophoretic technique to be implemented. The measurement method can be described as robust, reliable, and affordable enough for being adopted by researchers and companies devoted to electrophoretic μPADs and related technologies.

Immunomagnetic separation: An effective pretreatment technology for isolation and enrichment in food microorganisms detection

The high efficiency and accurate detection of foodborne pathogens and spoilage microorganisms in food are a task of great social, economic, and public health importance. However, the contamination levels of target bacteria in food samples are very low. Owing to the background interference of food ingredients and negative impact of nontarget flora, the establishment of efficient pretreatment techniques is very crucial for the detection of food microorganisms. With the significant advantages of high specificity and great separation efficiency, immunomagnetic separation (IMS) assay based on immunomagnetic particles (IMPs) has been considered as a powerful system for the separation and enrichment of target bacteria. This paper mainly focuses on the development of IMS as well as their application in food microorganisms detection. First, the basic principle of IMS in the concentration of food bacteria is presented. Second, the effect of different factors, including the sizes of magnetic particles (MPs), immobilization of antibody and operation parameters (the molar ratio of antibody to MPs, the amount of IMPs, incubation time, and bacteria concentration) on the immunocapture efficiency of IMPs are discussed. The performance of IMPs in different food samples is also evaluated. Finally, the combination of IMS and various kinds of detection methods (immunology-based methods, nucleic acid-based methods, fluorescence methods, and biosensors) to detect pathogenic and spoilage organisms is summarized. The challenges and future trends of IMS are also proposed. As an effective pretreatment technique, IMS can improve the detection sensitivity and shorten their testing time, thus exhibiting broad prospect in the field of food bacteria detection.

Bacterial Imprinting Methods and Their Applications: An Overview

Microbial contaminations and infections are hazardous and pose crucial concerns for humans. They result in severe morbidity and mortality around the globe. Even though dish-culturing, polymerase chain reaction (PCR), an enzyme-linked immunosorbent assay (ELISA) exhibits accurate and reliable detection of bacteria but these methods are time-consuming, laborious, and expensive. This warrants early detection and quantification of bacteria for timely diagnosis and treatment. Bacteria imprinting ensures a solution for selective and early detection of bacteria by snagging them inside their imprinted cavities. This review provides an insight into MIPs based bacterial detection strategies, challenges, and future perspectives.

Recombinase polymerase amplification-lateral flow (RPA-LF) assay combined with immunomagnetic separation for rapid visual detection of Vibrio parahaemolyticus in raw oysters

This study was the first attempt to optimize a recombinase polymerase amplification (RPA) and lateral flow (LF) assay combined with immunomagnetic separation (IMS) for the detection of Vibrio parahaemolyticus in raw oysters. The newly developed IMS-RPA-LF assay effectively combines sample preparation, amplification, and detection into a single platform. Under optimal conditions, the average capture efficiency (CE) for 10⁴ colony forming units (CFU)/mL of four V. parahaemolyticus strains with 0.4 mg of immunomagnetic beads within 45 min was 80.3%. After optimization, the RPA-LF assay was able to detect V. parahaemolyticus within 15 min, comprising DNA amplification with RPA for 10 min at 37 °C and visualization of the amplicons through LF strips for 5 min. The RPA-LF assay exhibited good specificity by showing a test line for eight V. parahaemolyticus strains with different serotypes but no cross-reaction with 12 non-V. parahaemolyticus bacteria. RPA-LF assay was found to be sensitive and detected as low as 10 pg genomic DNA of V. parahaemolyticus. For spiked oyster samples, the detection sensitivity of V. parahaemolyticus was improved to 2 CFU/g by IMS-RPA-LF after enrichment for 4 h; in contrast, the IMS-PCR method required 8 h. Hence, even when V. parahaemolyticus was present in very low numbers in samples, the IMS-RPA-LF assay could be completed within half a workday. Because of the high sensitivity, specificity, and speed of the IMS-RPA-LF assay, this newly developed method opens a novel pathway for rapid diagnostic screening of V. parahaemolyticus in seafood, which is an increasingly important health issue worldwide. Graphical abstract.

An ultrasensitive biosensor for colorimetric detection of Salmonella in large-volume sample using magnetic grid separation and platinum loaded zeolitic imidazolate Framework-8 nanocatalysts

Salmonella is the leading risk factor in food safety. Rapid, sensitive and accurate detection of Salmonella is a key to prevent and control the outbreaks of foodborne diseases caused by Salmonella. In this study, we reported a colorimetric biosensor for ultrasensitive detection of Salmonella Typhimurium using a magnetic grid separation column to efficiently separate target bacteria from large volume of sample and platinum loaded zeolitic imidazolate framework-8 (Pt@ZIF-8) nanocatalysts to effectively amplify biological signal. The target Salmonella cells in large volume of sample were first separated and concentrated using the magnetic grid separation column with immune magnetic particle chains, then conjugated with the immune Pt@ZIF-8 nanocatalysts to mimic peroxidase for catalysis of hydrogen peroxide-3,3',5,5'-tetramethylbenzidine, and finally determined by measuring the catalysate at characteristic wavelength of 450 nm. This proposed biosensor was able to separate ∼70% of target Salmonella cells from 50 mL of bacterial sample and quantitatively detect Salmonella from 10¹ to 10⁴ CFU/mL in 2.5 h with the lower detection limit of 11 CFU/mL. The mean recovery for Salmonella in spiked chicken carcass was about 109.8%. This new magnetic grid separation method was first time reported for efficient separation of target bacteria from very large volume of sample to greatly improve the sensitivity of this biosensor and could be used with various biosensing assays for practical applications in routine detection of foodborne pathogens without any bacterial pre-enrichment.