Photoluminescent Lateral-Flow Immunoassay Revealed by Graphene Oxide: Highly Sensitive Paper-Based Pathogen Detection

Serodiagnosis of multiple cancers using an extracellular protein kinase A autoantibody-based lateral flow platform

Extracellular protein kinase A autoantibody (ECPKA-AutoAb) has been suggested as a universal cancer biomarker due to its higher amounts in serum of several types of cancer patients than that of normal individuals. Herein, we first developed a lateral flow immunoassay (LFIA) tool, using a sandwich format, toward ECPKA-AutoAb in human serum. For this format, 3G2 as a capture antibody was identified using hybridoma technique and a series of screenings where it showed superior capacity to recognize Enzo PKA catalytic subunit alpha (Cα), compared to other PKA antibodies and antigens. Using these components, we performed sandwich ELISA toward a mimic and real sample of ECPKA-AutoAb. As per the results, limit of detection (LOD) was found to be 135 ng/mL and ECPKA-AutoAb levels were higher in various cancer patients than in normal individuals like previous studies. Based on these results, we applied this sandwich format into LFIA tool and found that the LOD of the fabricated LFIA tool showed about 3.8 ng/mL using spiked PKA-Ab, which is significantly improved compared to the LOD of sandwich ELISA. Also, the developed LFIA tool demonstrated a remarkable ability to detect significant differences in ECPKA-AutoAb levels between normal and cancer patients within 15 min, showing a potential for point-of-care (PoC) detection. One interesting point is that our LFIA strip contains an additional conjugation pad II, named because of its position behind the conjugation pad, in which PKA Cα is dried, enabling a sandwich format.

Nanotechnology in the Diagnosis and Treatment of Antibiotic-Resistant Infections

The development of antimicrobial resistance (AMR), along with the relative reduction in the production of new antimicrobials, significantly limits the therapeutic options in infectious diseases. Thus, novel treatments, especially in the current era, where AMR is increasing, are urgently needed. There are several ongoing studies on non-classical therapies for infectious diseases, such as bacteriophages, antimicrobial peptides, and nanotechnology, among others. Nanomaterials involve materials on the nanoscale that could be used in the diagnosis, treatment, and prevention of infectious diseases. This review provides an overview of the applications of nanotechnology in the diagnosis and treatment of infectious diseases from a clinician's perspective, with a focus on pathogens with AMR. Applications of nanomaterials in diagnosis, by taking advantage of their electrochemical, optic, magnetic, and fluorescent properties, are described. Moreover, the potential of metallic or organic nanoparticles (NPs) in the treatment of infections is also addressed. Finally, the potential use of NPs in the development of safe and efficient vaccines is also reviewed. Further studies are needed to prove the safety and efficacy of NPs that would facilitate their approval by regulatory authorities for clinical use.

Recent Advances in Optical Sensing for the Detection of Microbial Contaminants

Microbial contaminants are responsible for several infectious diseases, and they have been introduced as important potential food- and water-borne risk factors. They become a global burden due to their health and safety threats. In addition, their tendency to undergo mutations that result in antimicrobial resistance makes them difficult to treat. In this respect, rapid and reliable detection of microbial contaminants carries great significance, and this research area is explored as a rich subject within a dynamic state. Optical sensing serving as analytical devices enables simple usage, low-cost, rapid, and sensitive detection with the advantage of their miniaturization. From the point of view of microbial contaminants, on-site detection plays a crucial role, and portable, easy-applicable, and effective point-of-care (POC) devices offer high specificity and sensitivity. They serve as advanced on-site detection tools and are pioneers in next-generation sensing platforms. In this review, recent trends and advances in optical sensing to detect microbial contaminants were mainly discussed. The most innovative and popular optical sensing approaches were highlighted, and different optical sensing methodologies were explained by emphasizing their advantages and limitations. Consequently, the challenges and future perspectives were considered.

Micro-paper-based analytical device decorated with metal-organic frameworks for the assay of synthetic cannabinoids in oral fluids coupled to ion mobility spectrometry

A new concept of paper-based device has been developed combining the advantages of cellulose supports and the rich surface chemistry of metal-organic frameworks (MOFs). The composite, named as NH2-UiO-66@paper, has been developed for the isolation of synthetic cannabinoid receptor agonists (SCRAs) in oral fluids, trying to mimic the interactions of those compounds with the human CB1R and CB2R receptors, mainly governed by hydrogen bonding and π-interactions with serine and histidine residues. MOF selection (UiO-66) and functionalization of the ligand (2-aminoterephthalic acid) has been done according to the following criteria: (i) water stability of the selected MOF, and (ii) promoting appropriate interactions with SCRAs due to the MOF nature. NH2-UiO-66@paper composite has been characterized in depth and the results confirmed that the material is stable at the temperature selected for thermal desorption (230 °C). Furthermore, the developed method provided appropriate precision values (RSD < 12%) and a limit of detection as low as 10 ng using ion mobility spectrometry as analytical technique. Lastly, the method has been successfully applied to the isolation of several synthetic cannabinoids from oral fluids. This method claims to be an interesting approach for expanding the combination of MOFs with sustainable support and represents a promising alternative to sophisticated and non-portable systems due to the negligible sample treatment required and the simplicity of the operation, which can be applied with screening purposes.

Lateral flow immunoassays for antigens, antibodies and haptens detection

Lateral flow immunoassay (LFIA) is widely used as a rapid point-of-care testing (POCT) technique in food safety, veterinary and clinical detection on account of the accessible, fast and low-cost characteristics. After the outbreak of the coronavirus disease 2019 (COVID-19), different types of LFIAs have attracted considerable interest because of their ability of providing immediate diagnosis directly to users, thereby effectively controlling the outbreak. Based on the introduction of the principles and key components of LFIAs, this review focuses on the major detection formats of LFIAs for antigens, antibodies and haptens. With the rapid innovation of detection technologies, new trends of novel labels, multiplex and digital assays are increasingly integrated with LFIAs. Therefore, this review will also introduce the development of new trends of LFIAs as well as its future perspectives.

Lateral Flow Immunoassay for Proteins

Protein biomarkers are useful for disease diagnosis. Identification thereof using in vitro diagnostics such as lateral flow immunoassays (LFIAs) has attracted considerable attention due to their low cost and ease of use especially in the point of care setting. Current challenges, however, do remain with respect to material selection for each component in the device and the synergistic integration of these components to display detectable signals. This review explores the principle of LFIA for protein biomarkers, device components including biomaterials and labeling methods. Medical applications and commercial status are examined as well. This review highlights critical methodologies in the development of new LFIAs and their role in advancing healthcare worldwide.

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.

Carbon Dots in the Detection of Pathogenic Bacteria and Viruses

Bacterial and viruses pathogens are a significant hazard to human safety and health. In the imaging and detection of pathogenic microorganisms, the application of fluorescent nanoparticles is very useful. Carbon dots and quantum dots are preferred in this regard as labels, amplifiers, and/or electrode modifiers because of their outstanding features. However, precise diagnostics to identify numerous harmful bacteria simultaneously still face considerable hurdles, yet it is an inevitable issue. With the growing development of biosensors, nanoproduct-based bio-sensing has recently become one of the most promising methods for accurately identifying and quantifying various pathogens at low cost, high sensitivity, and selectivity, with time savings. The most recent applications of carbon dots in optical and electrochemical-based sensors are discussed in this review, along with some examples of pathogen sensors.HighlightsSimultaneous and early detection of pathogens is a critical issue in the management of readily spread to prevent epidemics.Carbon dots-based biosensors are more preferred in detection of pathogens due to high selectivity and sensitivity, as well as quick and cheap point-of-care platform.Summary of recent advances in the design of optical and electrochemical biosensors for the detection of pathogens.

A Universal Bacterial Catcher Au-PMBA-Nanocrab-Based Lateral Flow Immunoassay for Rapid Pathogens Detection

In traditional lateral flow immunoassays (LFIA) for pathogens detection, capture antibody (CA) is necessary and usually conjugated to Au nanoparticles (NPs) in order to label the target analyte. However, the acquisition process of the Au-CA nanoprobe is relatively complicated and costly, which will limit the application of LFIA. Herein, p-mercaptophenylboronic acid-modified Au NPs (namely Au-PMBA nanocrabs), were synthesized and applied for a new CA-independent LFIA method. The stable Au-PMBA nanocrabs showed outstanding capability to capture both Gram-negative bacteria and Gram-positive bacteria through covalent bonding. The acquired Au-PMBA-bacteria complexes were dropped onto the strip, and then captured by the detection antibody on the test line (T-line). Take Escherichia coli O157:H7 as an example, the gray value of T-line was proportional to the bacteria concentration and the linear range was 10³-10⁷ cfu·mL^-1. This CA-independent strategy exhibited higher sensitivity than the traditional CA-dependent double antibody sandwich method, because detection limit of the former one was 10³ cfu·mL^-1 only by visual observation, which was reduced by 3 orders of magnitude. Besides, this platform successfully screened E. coli O157:H7 in four food samples with recoveries ranging from 90.25% to 107.25%. This CA-independent LFIA showed great advantages and satisfactory potential for rapid foodborne pathogens detection in real samples.

State of the art: Lateral flow assays toward the point-of-care foodborne pathogenic bacteria detection in food samples

Diverse chemicals and some physical phenomena recently introduced in nanotechnology have enabled scientists to develop useful devices in the field of food sciences. Concerning such developments, detecting foodborne pathogenic bacteria is now an important issue. These kinds of bacteria species have demonstrated severe health effects after consuming foods and high mortality related to acute cases. The most leading path of intoxication and infection has been through food matrices. Hence, quick recognition of foodborne bacteria agents at low concentrations has been required in current diagnostics. Lateral flow assays (LFAs) are one of the urgent and prevalently applied quick recognition methods that have been settled for recognizing diverse types of analytes. Thus, the present review has stressed on latest developments in LFAs-based platforms to detect various foodborne pathogenic bacteria such as Salmonella, Listeria, Escherichia coli, Brucella, Shigella, Staphylococcus aureus, Clostridium botulinum, and Vibrio cholera. Proper prominence has been given on exactly how the labels, detection elements, or procedures have affected recent developments in the evaluation of diverse bacteria using LFAs. Additionally, the modifications in assays specificity and sensitivity consistent with applied food processing techniques have been discussed. Finally, a conclusion has been drawn for highlighting the main challenges confronted through this method and offered a view and insight of thoughts for its further development in the future.

Lateral flow immunoassay based on dual spectral-overlapped fluorescence quenching of polydopamine nanospheres for sensitive detection of sulfamethazine

Herein, we propose a lateral flow immunoassay (LFIA) based on the dual spectral-overlapped fluorescence quenching of polydopamine nanospheres (PDANs) caused by the inner filter effect to sensitively detect sulfamethazine (SMZ). The fluorescence quenching LFIA device consists of four parts: absorbent pad, polyvinyl chloride pad, sample pad, and nitrocellulose membrane. Compared with traditional quenchers such as gold nanoparticles (AuNPs) with single spectral-overlapped quenching ability, PDANs can quench the excitation light and emission light of three fluorescence donors (aggregation-induced emission fluorescent microsphere, AIEFM; fluorescent microsphere, FM; and quantum dot bead, QB). The fluorescence intensity changes (ΔF) are numerically larger for PDANs-LFIA (ΔF_AIEFM = 2315, ΔF_FM = 979, ΔF_QB = 910) than those for AuNPs-LFIA (ΔF_AIEFM = 1722, ΔF_FM = 833, ΔF_QB =;520). AIEFM-based PDANs-LFIA exhibits a large ΔF (2315) in response to the changes in the SMZ concentration, and produces a high signal-to-noise ratio. The limit of detection (LOD) and visual LOD of LFIA based on PDANs quenching AIEFM for the detection of SMZ in chicken are 0.043 and 0.5 ng/mL, respectively. The results confirm that the proposed method can be used for the detection of hazardous materials in practical applications.

Photoluminescent Molecules and Materials as Diagnostic Reporters in Lateral Flow Assays

The lateral flow assay (LFA) is a point-of-care diagnostic test commonly available in an over-the-counter format because of its simplicity, speed, low cost, and portability. The reporter particles in these assays are among their most significant components because they perform the diagnostic readout and dictate the test's sensitivity. Today, gold nanoparticles are frequently used as reporters, but recent work focusing on photoluminescent-based reporter technologies has pushed LFAs to better performance. These efforts have focused specifically on reporters made of organic fluorophores, quantum dots, lanthanide chelates, persistent luminescent phosphors, and upconversion phosphors. In most cases, photoluminescent reporters show enhanced sensitivity compared to conventional gold nanoparticle-based assays. Here, we examine the advantages and disadvantages of these different reporters and highlight their potential benefits in LFAs. Our assessment shows that photoluminescent-based LFAs can not only reach lower detection limits than LFAs with traditional reporters, but they also can be capable of quantitative and multiplex analyte detection. As a result, the photoluminescent reporters make LFAs well-suited for medical diagnostics, the food and agricultural industry, and environmental testing.

Recent Advances and Applications in Paper-Based Devices for Point-of-Care Testing

Point-of-care testing (POCT), as a portable and user-friendly technology, can obtain accurate test results immediately at the sampling point. Nowadays, microfluidic paper-based analysis devices (μPads) have attracted the eye of the public and accelerated the development of POCT. A variety of detection methods are combined with μPads to realize precise, rapid and sensitive POCT. This article mainly introduced the development of electrochemistry and optical detection methods on μPads for POCT and their applications on disease analysis, environmental monitoring and food control in the past 5 years. Finally, the challenges and future development prospects of μPads for POCT were discussed.

Rapid and sensitive detection of Salmonella in milk based on hybridization chain reaction and graphene oxide fluorescence platform

Salmonella is a foodborne pathogen that has contributed to numerous food safety accidents worldwide, making it necessary to detect contamination at an early stage. A pair of specific primers based on the invA gene of Salmonella was designed for PCR. Target double-stranded DNA (dsDNA) from PCR was purified and denatured at high temperature to obtain target single-stranded DNA (ssDNA). Two carboxyfluorescein-labeled hairpin probes (H1-FAM and H2-FAM) were designed with complementary portions to the ssDNA sequence so that binding could trigger H1-FAM and H2-FAM hybridization chain reaction (HCR) to produce a long dsDNA complex. In this study, graphene oxide (GO) was used in the development of a homogeneous fluorescence detection platform for Salmonella. Using this HCR-GO assay platform, Salmonella detection was completed in 3.5 h. Salmonella was reliably and specifically detected with a limit of detection (LOD) of 4.2 × 10¹ cfu/mL in pure culture. Moreover, this new HCR-GO assay platform was successfully applied to the detection of Salmonella in artificially contaminated milk with a LOD of 4.2 × 10² cfu/mL.

Nanomaterial application in bio/sensors for the detection of infectious diseases

Infectious diseases are a potential risk for public health and the global economy. Fast and accurate detection of the pathogens that cause these infections is important to avoid the transmission of the diseases. Conventional methods for the detection of these microorganisms are time-consuming, costly, and not applicable for on-site monitoring. Biosensors can provide a fast, reliable, and point of care diagnostic. Nanomaterials, due to their outstanding electrical, chemical, and optical features, have become key players in the area of biosensors. This review will cover different nanomaterials that employed in electrochemical, optical, and instrumental biosensors for infectious disease diagnosis and how these contributed to enhancing the sensitivity and rapidity of the various sensing platforms. Examples of nanomaterial synthesis methods as well as a comprehensive description of their properties are explained. Moreover, when available, comparative data, in the presence and absence of the nanomaterials, have been reported to further highlight how the usage of nanomaterials enhances the performances of the sensor.

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.

Commercially available rapid diagnostic tests for the detection of high priority pathogens: status and challenges

The ongoing COVID-19 pandemic has shown the importance of having analytical devices that allow a simple, fast, and robust detection of pathogens which cause epidemics and pandemics. The information these devices can collect is crucial for health authorities to make effective decisions to contain the disease's advance. The World Health Organization published a list of primary pathogens that have raised concern as potential causes of future pandemics. Unfortunately, there are no rapid diagnostic tests commercially available and approved by the regulatory bodies to detect most of the pathogens listed by the WHO. This report describes these pathogens, the available detection methods, and highlights areas where more attention is needed to produce rapid diagnostic tests for future pandemic surveillance.

Lateral flow device for water fecal pollution assessment: from troubleshooting of its microfluidics using bioluminescence to colorimetric monitoring of generic Escherichia coli

Water is the most important ingredient of life. Water fecal pollution threatens water quality worldwide and has direct detrimental effects on human health and the global economy. Nowadays, assessment of water fecal pollution relies on time-consuming techniques that often require well-trained personnel and highly-equipped laboratories. Therefore, faster, cheaper, and easily-used systems are needed to in situ monitor water fecal pollution. Herein, we have developed colorimetric lateral flow strips (LFS) able to detect and quantify Escherichia coli species in tap, river, and sewage water samples as an indicator of fecal pollution. The combination of LFS with a simple water filtration unit and a commercially available colorimetric reader enhanced the assay sensitivity and enabled more accurate quantification of bacteria concentration down to 104 CFU mL-1 in 10 minutes, yielding recovery percentages between 80% and 90% for all water samples analyzed. Overall, this system allows for monitoring and assessing water quality based on E. coli species as a standard microbiological indicator of fecal pollution. Furthermore, we have developed a novel bioluminescent, bacteria-based method to quickly characterize the performance of a great variety of LFS materials. This new method allows evaluating the flow rate of big analytes such as bacteria through the LFS materials, as a suggestive means for selecting the appropriate materials for fabricating LFS targeting big analytes (≈2 μm). As a whole, the proposed approach can accelerate and reduce the costs of water quality monitoring and pave the way for further improvement of fecal pollution detection systems.

The Microbiome Meets Nanotechnology: Opportunities and Challenges in Developing New Diagnostic Devices

Monitoring of the human microbiome is an emerging area of diagnostics for personalized medicine. Here, the potential of different nanomaterials and nanobiosensing technologies is reviewed for the development of novel diagnostic devices for the detection and measurement of microbiome-related biomarkers. Moreover, the current and future landscape of microbiome-based diagnostics is defined by exploring the advantages and disadvantages of current nanotechnology-based approaches, especially in the context of developing point-of-care (PoC) devices that would meet the international guidelines known as REASSURED (Real-time connectivity; Ease of specimen collection; Affordability; Sensitivity; Specificity; User-friendliness; Rapid & robust operation; Equipment-free; and Deliverability). Finally, the strategies of the latest international scientific consortia working in this field are analyzed, the current microbiome diagnostics market are reported and the principal ethical, legal, and societal issues related to microbiome R&D and innovation are discussed.

Paper-Based Biosensors: Frontiers in Point-of-Care Detection of COVID-19 Disease

This review summarizes the state of the art of paper-based biosensors (PBBs) for coronavirus disease 2019 (COVID-19) detection. Three categories of PBB are currently being been used for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) diagnostics, namely for viral gene, viral antigen and antibody detection. The characteristics, the analytical performance, the advantages and drawbacks of each type of biosensor are highlighted and compared with traditional methods. It is hoped that this review will be useful for scientists for the development of novel PBB platforms with enhanced performance for helping to contain the COVID-19 outbreak, by allowing early diagnosis at the point of care (POC).

A simple paper-based colorimetric analytical device for rapid detection of Enterococcus faecalis under the stress of chlorophenols

Bacteria detection and toxicity measurement are essential in many aspects. Becoming increasingly popular in recent years, paper-based analytical devices (PADs) have proven to be cost-effective, portable and eco-friendly with quantitative diagnostic results. In this work, by a straightforward soaking-drying method, a resazurin-deposited PAD has been developed for rapid bacteria detection and biotoxicity measurement. The colorimetric response on the PAD was generated from metabolic reduction of resazurin by Enterococcus faecalis, a facultative anaerobic bacterial strain. After recording and quantifying the colorimetric response with Hue value by a smartphone, the bioassay on PAD enables the detection of resazurin reduction kinetics difference among bacteria at various densities in 10 min. Thereby, the bioassay on PAD was applied to study the toxicity of two chlorophenols, i.e. pentachlorophenol (PCP) and 4-chlorophenol (4-CP), to E. faecalis. Compared to growth-based inhibition test, which takes 5 h, this assay shows higher efficiency, i.e. in 30 min, the biotoxicity difference between PCP and 4-CP can be identified.

Emerging graphene-based sensors for the detection of food adulterants and toxicants - A review

The detection of food adulterants and toxicants can prevent a large variety of adverse health conditions for the global population. Through the process of rapid sensing enabled by deploying novel and robust sensors, the food industry can assist in the detection of adulterants and toxicants at trace levels. Sensor platforms which exploit graphene-based nanomaterials satisfy this requirement due to outstanding electrical, optical and thermal properties. The materials' facile conjugation with linkers and biomolecules along with the option for further enhancement using nanoparticles results in highly sensitive and selective sensing characteristics. This review highlights novel applications of graphene derivatives for detection covering three important approaches; optical, electrical (field-effect) and electrochemical sensing. Suitable graphene-based sensors for portable devices as point-of-need platforms are also presented. The future scope of these sensors is discussed to showcase how these emerging techniques will disrupt the food detection sector for years to come.

Lateral flow immunoassay for furazolidone point-of-care testing: Cater to the call of saving time, labor, and cost by coomassie brilliant blue labeling

Furazolidone (FZD) and its metabolite called 3-amino-2-oxazolidinone (AOZ) would induce carcinogenic and mutagenic effects to human. In this work, to develop a novel, stable, and simple point of care testing (POCT) with a potential to social applied for FZD detection, we utilized the aspect of protein staining of coomassie brilliant blue (CBB) to exploit a new CBB-LFIA strategy free of NPs. Only one mixing step is needed during the probe manufacturing process, which requires just 2 h and is a great time saving strategy compared with other methods (requiring 4-33 h for probe preparation). Besides, the cost of CBB-LFIA is 300 times lesser than other LFIA with respect to obtaining the label. The developed CBB-LFIA was successfully applied to detect AOZ with a detection limit of 2 ng mL^-1, without any influence from other potential interfering compounds. The proposed CBB-LFIA exhibited prominent practical application, and possesses considerable utilization potential in the related field.

PARAFAC study of L-cys@CdTe QDs interaction to BSA, cytochrome c and trypsin: An approach through electrostatic and covalent bonds

Utilizing fluorescence spectroscopy, non-covalent and covalent interactions of L-cys@CdTe quantum dots to bovine serum albumin (BSA), cytochrome c and trypsin were investigated. L-cys@CdTe QDs with the emission maximum at 530 nm and an average diameter of 2.6 nm were synthesized in the aqueous medium. Formaldehyde, N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDC) with N-hydroxysuccinimide (NHS), and glutaraldehyde was applied as cross-linkers. In the case of both electrostatic and covalent strategies PARAFAC, as a powerful multi-way chemometrics technique, was utilized to analyze fluorescence excitation-emission (EEM) spectra. For non-covalent and covalent bonding, two and three significant components composed the PARAFAC models. Resolved EEM shows that in the presence of formaldehyde, a new component with an emission peak similar to BSA was obtained. Using EDC-NHS cross-linker, the fluorescence peak of the newly formed component was in a distinct wavelength with similar emission intensity, compared to L-cys@CdTe QDs and BSA. Employing glutaraldehyde, a distinguished component was easily detected at emission wavelengths higher than that of L-cys@CdTe QDs and proteins. It was concluded that the choice of cross-linker is a critical step to create different emission spectra when dealing with nano-bio-conjugations. This study shows that glutaraldehyde cross-linker leads to increase sensitivity, selectivity, and accuracy of protein analysis.

Binding enhancements of antibody functionalized natural and synthetic fibers

Development of low cost biosensing using convenient and environmentally benign materials is important for wide adoption and ultimately improved healthcare and sustainable development. Immobilized antibodies are often incorporated as an essential biorecognition element in point-of-care biosensors but these proteins are costly. We present a strategy of combining convenient and low-cost surface functionalization approaches for increasing the overall binding activity of antibody functionalized natural and synthetic fibers. We demonstrate a simple one-step in situ silica NP growth protocol for increasing the surface area available for functionalization on cotton and polyester fabrics as well as on nanoporous cellulose substrates. Comparing this effect with the widely adopted and low cost plant-based polyphenol coating to enhance antibody immobilization, we find that both approaches can similarly increase overall surface activity, and we illustrate conditions under which the two approaches can produce an additive effect. Furthermore, we introduce co-immobilization of antibodies with a sacrificial “steric helper” protein for further enhancing surface activities. In combination, several hundred percent higher activities compared to physical adsorption can be achieved while maintaining a low amount of antibodies used, thus paving a practical path towards low cost biosensing.

Cotton, nanoporous cellulose and polyester fabric surfaces are functionalized with combinations of in situ grown silica NPs, polyphenol coating, and protein co-immobilization to enhance surface area, antibody binding efficiency, and biosensing.

Recent advances in sensitivity enhancement for lateral flow assay

Conventional lateral flow assay (LFA) is typically performed by observing the color changes in the test lines by naked eyes, which achieves considerable commercial success and has a significant impact on the fields of food safety, environment monitoring, disease diagnosis, and other applications. However, this qualitative detection method is not very suitable for low levels of disease biomarkers' detection. Although many nanomaterials are used as new labels for LFA, additional readers limit their application to some extent. Fortunately, a lot of work has been done for improving the sensitivity of LFA. In this review, currently reported LFA sensitivity enhancement methods with an objective evaluation are summarized, such as sample pretreatment, the change of flow rate, and label evolution, and future development direction and challenges of LFAs are discussed.

Rapid and highly sensitive detection of Salmonella typhimurium in lettuce by using magnetic fluorescent nanoparticles

The highly efficient detection of Salmonella typhimurium (S. typhimurium), a common foodborne bacterial, is important for the safety assurance of leafy vegetables. In this study, a fluorescent sensor (FMNCs-Apt), based on Fe3O4 magnetic nanoparticles and aptamer-modified carbon quantum dots, was developed for the rapid and highly sensitive detection of S. typhimurium in lettuce. First, carbon quantum dots were covalently bonded to the surface of prepared Fe3O4@chitosan to form magnetic fluorescence composite nanoparticles (FMNCs). Then, the aptamers of S. typhimurium were covalently linked to the surface (and named FMNCs-Apt). Fluorescence intensity of the FMNCs-Apt probes decreased as they aggregated on the surface of the bacteria, and the aggregation was separated using a magnet. Under the optimal conditions, the fluorescence change values of the solution showed a good linear relationship with the concentration of Salmonella (103-106 CFU mL-1). The detection limit of the method is 100 CFU mL-1 and 138 CFU mL-1 in fresh-cut vegetable washing solution and lettuce sample, respectively. Accordingly, this developed fluorescent probe became a highly sensitive and efficient sensor for the rapid detection of S. typhimurium in lettuce.

A Comparative Study of Approaches to Improve the Sensitivity of Lateral Flow Immunoassay of the Antibiotic Lincomycin

This study provides a comparative assessment of the various nanodispersed markers and related detection techniques used in the immunochromatographic detection of an antibiotic lincomycin (LIN). Improving the sensitivity of the competitive lateral flow immunoassay is important, given the increasing demands for the monitoring of chemical contaminants in food. Gold nanoparticles (AuNPs) and CdSe/ZnS quantum dots (QDs) were used for the development and comparison of three approaches for the lateral flow immunoassay (LFIA) of LIN, namely, colorimetric, fluorescence, and surface-enhanced Raman spectroscopy (SERS)-based LFIAs. It was demonstrated that, for colorimetric and fluorescence analysis, the detection limits were comparable at 0.4 and 0.2 ng/mL, respectively. A SERS-based method allowed achieving the gain of five orders of magnitude in the assay sensitivity (1.4 fg/mL) compared to conventional LFIAs. Therefore, an integration of a SERS reporter into the LFIA is a promising tool for extremely sensitive quantitative detection of target analytes. However, implementation of this time-consuming technique requires expensive equipment and skilled personnel. In contrast, conventional AuNP- and QD-based LFIAs can provide simple, rapid, and inexpensive point-of-care testing for practical use.

Tutorial: design and fabrication of nanoparticle-based lateral-flow immunoassays

Lateral-flow assays (LFAs) are quick, simple and cheap assays to analyze various samples at the point of care or in the field, making them one of the most widespread biosensors currently available. They have been successfully employed for the detection of a myriad of different targets (ranging from atoms up to whole cells) in all type of samples (including water, blood, foodstuff and environmental samples). Their operation relies on the capillary flow of the sample throughout a series of sequential pads, each with different functionalities aiming to generate a signal to indicate the absence/presence (and, in some cases, the concentration) of the analyte of interest. To have a user-friendly operation, their development requires the optimization of multiple, interconnected parameters that may overwhelm new developers. In this tutorial, we provide the readers with: (i) the basic knowledge to understand the principles governing an LFA and to take informed decisions during lateral flow strip design and fabrication, (ii) a roadmap for optimal LFA development independent of the specific application, (iii) a step-by-step example procedure for the assembly and operation of an LF strip for the detection of human IgG and (iv) an extensive troubleshooting section addressing the most frequent issues in designing, assembling and using LFAs. By changing only the receptors, the provided example procedure can easily be adapted for cost-efficient detection of a broad variety of targets.

Point-of-Need Diagnostics for Foodborne Pathogen Screening

Foodborne illness is a major public health issue that results in millions of global infections annually. The burden of such illness sits mostly with developing countries, as access to advanced laboratory equipment and skilled lab technicians, as well as consistent power sources, is limited and expensive. Current gold standards in foodborne pathogen screening involve labor-intensive sample enrichment steps, pathogen isolation and purification, and costly readout machinery. Overall, time to detection can take multiple days, excluding the time it takes to ship samples to off-site laboratories. Efforts have been made to simplify the workflow of such tests by integrating multiple steps of foodborne pathogen screening procedures into a singular device, as well as implementing more point-of-need readout methods. In this review, we explore recent advancements in developing point-of-need devices for foodborne pathogen screening. We discuss the detection of surface markers, nucleic acids, and metabolic products using both paper-based and microfluidic devices, focusing primarily on developments that have been made between 2015 and mid-2020.

Multiplexed tri-mode visual outputs of immunoassay signals on a clip-magazine-assembled photothermal biosensing disk

The photothermal biosensing principle is of increasing interest for point-of-care detection, but has rarely been applied in portable analytical devices in a lab-on-a-chip format. Herein, a photothermally responsive poly (methyl methacrylate) (PMMA)/paper hybrid disk (PT-Disk) was developed as a novel photothermal immunoassay device with the integration of a clip-magazine-assembled photothermal biosensing strategy. The PT-Disk consisted of a dissociative thermoresponsive hydrogel-loaded clip unit where the sandwich-type immunoreaction with an iron oxide-to-Prussian blue nanoparticle (PB NP) conversion took place and a magazine bearer for the rotational clip assembly and visual signal outputs. Upon laser irradiation of the clip-magazine-assembled PT-Disk, on-chip photothermal effect of PB NPs triggered both dose-dependent temperature elevation and the subsequent release of dye solutions from the central clip unit to surrounding magazine-bearing paper channels as the result of phase transition of the hydrogels, realizing multiplexed thermal image- and distance-based visual quantitative signal outputs in combination with the preliminary colorimetric readout on the PT-Disk. Using the multiplexed tri-mode signal outputs, the PT-Disk can quantify prostate specific antigen with limits of detection of 1.4-2.8 ng mL^-1. This is the first attempt to apply the photothermal biosensing principle in portable PMMA/paper-based analytical devices, which offers not only versatile on-chip visual quantitative signal outputs, but also the implementation of the photothermal biosensing principle in a lab-on-a-chip format.

Combating Actions of Green 2D-Materials on Gram Positive and Negative Bacteria and Enveloped Viruses

Interactions of novel bi-dimensional nanomaterials and live matter such as bacteria and viruses represent an extremely hot topic due to the unique properties of the innovative nanomaterials, capable in some cases to exhibit bactericide and antiviral actions. The interactions between bacteria and viruses and two dimensional nanosheets are here investigated. We extensively studied the interaction between a gram-negative bacterium, Escherichia coli, and a gram-positive bacterium, Staphylococcus aureus, with two different types of 2D nanoflakes such as MoS₂, belonging to the Transition Metal Dichalcogenides family, and Graphene Oxide. The same two types of nanomaterials were employed to study their antiviral action toward the Herpes simplex virus type-1, (HSV-1). The experimental results showed different bactericide impacts as well as different antiviral power between the two nanomaterials. The experimental findings were interpreted in bacteria on the base of the Derjaguin–Landau–Verwey–Overbeek theory. A simple kinetic model of bacterial growth in the presence of the interacting nanosheets is also elaborated, to explain the observed results. The experimental results in viruses are really novel and somewhat surprising, evidencing a stronger antiviral action of Graphene Oxide as compared to MoS₂. Results in viruses are complicated to quantitatively interpret due to the complexity of the system under study, constituted by virus/host cell and nanoflake, and due to the lack of a well assessed theoretical context to refer to. Thus, these results are interpreted in terms of qualitative arguments based on the chemical properties of the interactors in the given solvent medium.

Optimization of paper-based nanoparticle immunoassays for direct detection of the bacterial pathogen V. parahaemolyticus in oyster hemolymph

The detection of foodborne pathogens is critical for disease control and infection prevention, especially in seafood consumed raw or undercooked. Paper-based diagnostic tools are promising for rapid fieldable detection and provide a readout by eye due to the use of gold nanoparticle immunoprobes. Here we study different strategies to overcome these challenges in a real biological matrix, oyster hemolymph, for the detection of the pathogenic bacteria Vibrio parahaemolyticus (Vp). Nanoparticle surface chemistry, nitrocellulose speed and blocking, running steps, and antibody concentrations on the NP and nitrocellulose were all studied. Their effect on paper immunoassay signal intensity was quantified to determine optimal conditions, which enabled the detection of Vp directly from hemolymph below pathogenic concentrations.

Functional nanozyme mediated multi-readout and label-free lateral flow immunoassay for rapid detection of Escherichia coli O157:H7

To overcome the drawbacks of antibody labeling dependence and single-readout system in the conventional lateral flow immunoassays (LFIAs) as well as the non-targeted combination of new capture agents reported recently for pathogen detection, in this work, a multi-readout and label-free LFIA was proposed for rapid detection of Escherichia coli O157:H7 (E. coli O157:H7) based on a nanozyme-bacteria-antibody sandwich pattern. A type of functional nanozyme-mannose modified Prussian blue (man-PB), was introduced as the recognition agent as well as signal indicator. Apart from original signal intensity on the T-line, the peroxidase-like catalytic activity-driven generation of colorimetric signal could be used as another format of quantitation. Importantly, such LFIA could exhibit excellent performance for target pathogens detection separately with a quantitative range of 10²-10⁸ cfu·mL^-1 and a low detection limit of 10² cfu·mL^-1 based on different readout formats, indicating the application potential of the proposed LFIA in real samples.

Functional nanomaterials based immunological detection of aflatoxin B1: a review

Aflatoxin B1 (AFB1) is highly carcinogenic, mutagenic and teratogenic. Accordingly, sensitive, rapid and cost-effective techniques for detection of AFB1 is in urgent demand for food safety and the health of consumers. In this review, we report the current state of immunoassay formats and development, mainly based on nanomaterials for determination of AFB1. Following an introduction of the field, the microplate-, membrane- and microelectrode-based immunoassays are described. The relevant mechanisms, sensitivities, superiorities and deficiencies of each format are discussed. Finally, perspectives on the future development of nanomaterials-based immunoassays for AFB1 are provided.

Lab in a Tube: Point-of-Care Detection of Escherichia coli

Significant levels of infectious diseases caused by pathogenic bacteria are nowadays a worldwide matter, carrying considerable public health care challenges and huge economic concerns. Because of the rapid transmission of these biothreat agents and the outbreak of diseases, a rapid detection of pathogens in early stages is crucial, particularly in low-resources settings. To this aim, we developed for the first time a new sensing approach carried out in a single step for Escherichia coli O157:H7 detection. The detection principle is based on Förster resonance energy transfer using gold nanoclusters as a signal reporter and gold nanoparticles conjugated with antibodies as a quencher. The sensing platform includes an ultraviolet-light-emitting diode to provide the proper excitation and consists of a microtube containing two pieces of fiber glass; one of them is embedded with label-free gold nanoclusters and the other one with gold nanoparticles conjugated with antibodies. Upon the addition of the sample containing bacteria, the florescence of gold nanoclusters is recovered. The assay was evaluated by the naked eye (on/off) and quantitatively with use of a smartphone camera. The biosensor proved to be highly specific and sensitive, achieving a limit of detection as low as 4.0 cfu mL^-1. Additionally, recoveries of 110% and 95% were obtained when the platforms in spiked river and tap water, respectively, were evaluated.

Recent advances in high-sensitivity detection methods for paper-based lateral-flow assay

Paper-based lateral-flow assays (LFAs) have achieved considerable commercial success and continue to have a significant impact on medical diagnostics and environmental monitoring. Conventional LFAs are typically performed by examining the color changes in the test bands by naked eye. However, for critical biochemical markers that are present in extremely small amounts in the clinical specimens, this readout method is not quantitative, and does not provide sufficient sensitivity or suitable detection limit for a reliable assay. Diverse technologies for high-sensitivity LFA detection have been developed and commercialization efforts are underway. In this review, we aim to provide a critical and objective overview of the recent progress in high-sensitivity LFA detection technologies, which involve the exploitation of the physical and chemical responses of transducing particles. The features and biomedical applications of the technologies, along with future prospects and challenges, are also discussed.

Recent advances in cellulose-based membranes for their sensing applications

ABSTRACT

In recent years, sensing applications have played a very important role in various fields. As a novel natural material, cellulose-based membranes with many merits can be served as all kinds of sensors. This review summarizes the recent progress of cellulose membranes as sensors, mainly focusing on their preparation processes and sensing properties. In addition, the opportunities and challenges of cellulose membrane-based sensors are also prospected. This review provides some references for the design of cellulose membrane materials for sensing applications in the future.