Fluorescence-based bioassays for the detection and evaluation of food materials

Mesoporous Silica Nanoparticles-Enhanced Microarray Technology for Highly Sensitive Simultaneous Detection of Multiplex Foodborne Pathogens

Ensuring food safety is paramount for the food industry and global health concerns. In this study, we have developed a method for the detection of prevalent foodborne pathogenic bacteria, including Escherichia coli, Salmonella spp., Listeria spp., Shigella spp., Campylobacter spp., Clostridium spp., and Vibrio spp., utilizing antibody-aptamer arrays. To enhance the fluorescence signals on the microarray, the mesoporous silica nanoparticles (MSNs) conjugated with fluorescein, streptavidin, and seven detection antibodies-biotin were employed, forming fluorescein doped mesoporous silica nanoparticles conjugated with detection antibodies (MSNs-Flu-SA-Abs) complexes. The array pattern was designed for easy readability and enabled the simultaneous detection of all seven foodborne pathogens, referred to as the 7FP-biochip. Following the optimization of MSNs-Flu-SA-Abs complexes attachment and enhancement of the detection signal in fluorescent immunoassays, a high level of sensitivity was achieved. The detection limits for the seven pathogens in both buffer and food samples were 102 CFU/mL through visual screening, with fluorescent intensity quantification achieving levels as low as 20-34 CFU/g were achieved on the antibody-aptamer arrays. Our antibody-aptamer array offers several advantages, including significantly reduced nonspecific binding with no cross-reaction between bacteria. Importantly, our platform detection exhibited no cross-reactivity among the tested bacteria in this study. The multiplex detection of foodborne pathogens in canned tuna samples with spiked bacteria was successfully demonstrated in real food measurements. In conclusion, our study presents a promising method for detecting multiple foodborne pathogens simultaneously. With its high sensitivity and specificity, the developed antibody-aptamer array holds great potential for enhancing food safety and public health.

Comprehensive fluorescence profiles of contamination-prone foods applied to the design of microcontact-printed in situ functional oligonucleotide sensors

With both foodborne illness and food spoilage detrimentally impacting human health and the economy, there is growing interest in the development of in situ sensors that offer real-time monitoring of food quality within enclosed food packages. While oligonucleotide-based fluorescent sensors have illustrated significant promise, the development of such on-food sensors requires consideration towards sensing-relevant fluorescence properties of target food products-information that has not yet been reported. To address this need, comprehensive fluorescence profiles for various contamination-prone food products are established in this study across several wavelengths and timepoints. The intensity of these food backgrounds is further contextualized to biomolecule-mediated sensing using overlaid fluorescent oligonucleotide arrays, which offer perspective towards the viability of distinct wavelengths and fluorophores for in situ food monitoring. Results show that biosensing in the Cyanine3 range is optimal for all tested foods, with the Cyanine5 range offering comparable performance with meat products specifically. Moreover, recognizing that mass fabrication of on-food sensors requires rapid and simple deposition of sensing agents onto packaging substrates, RNA-cleaving fluorescent nucleic acid probes are successfully deposited via microcontact printing for the first time. Direct incorporation onto food packaging yields cost-effective sensors with performance comparable to ones produced using conventional deposition strategies.

A review on recent advances in assays for DNMT1: a promising diagnostic biomarker for multiple human cancers

The abnormal expression of human DNA methyltransferases (DNMTs) is closely related with the occurrence and development of a wide range of human cancers. DNA (cytosine-5)-methyltransferase-1 (DNMT1) is the most abundant human DNA methyltransferase and is mainly responsible for genomic DNA methylation patterns. Abnormal expression of DNMT1 has been found in many kinds of tumors, and DNMT1 has become a valuable target for the diagnosis and drug therapy of diseases. Nowadays, DNMT1 has been found to be involved in multiple cancers such as pancreatic cancer, breast cancer, bladder cancer, lung cancer, gastric cancer and other cancers. In order to achieve early diagnosis and for scientific research, various analytical methods have been developed for qualitative or quantitative detection of low-abundance DNMT1 in biological samples and human tumor cells. Herein, we provide a brief explication of the research progress of DNMT1 involved in various cancer types. In addition, this review focuses on the types, principles, and applications of DNMT1 detection methods, and discusses the challenges and potential future directions of DNMT1 detection.

Recent advances in liposome development for studying protein-lipid interactions

Protein-lipid interactions are crucial for various cellular biological processes like intracellular signaling, membrane transport, and cytoskeletal dynamics. Therefore, studying these interactions is essential to understand and unravel their specific functions. Nevertheless, the interacting proteins of many lipids are poorly understood and still require systematic study. Liposomes are the most well-known and familiar biomimetic systems used to study protein-lipid interactions. Although liposomes have been widely used for studying protein-lipid interactions in classical methods such as the co-flotation assay (CFA), co-sedimentation assay (CSA), and flow cytometric assay (FCA), an overview of their current applications and developments in high-throughput methods is not yet available. Here, we summarize the liposome development in low and high-throughput methods to study protein-lipid interactions. Besides, a constructive comment for each platform is presented to stimulate the advancement of these technologies in the future.

Metal-Chelated Polymeric Nanomaterials for the Removal of Penicillin G Contamination

We developed selective and relatively low-cost metal-chelated nanoparticle systems for the removal of the penicillin G (Pen G) antibiotic, presented for the first time in the literature. In the nanosystem, poly(glycidyl methacrylate) nanoparticles were synthesized by a surfactant-free emulsion polymerization method and covalently bound with a tridentate-chelating ligand, iminodiacetic acid, based on the immobilized metal chelate affinity technique. It was modified with Cu²⁺, a chelating metal, to make Pen G specific. Metal-chelated nanoparticles were characterized by Fourier-transform infrared spectroscopy, energy dispersive spectrometry, zeta dimensional analysis, and scanning electron microscopy technology. Optimization studies of the Pen G removal were conducted. As a result of this study, Pen G removal with the p(GMA)-IDA-Cu²⁺ nanoparticle reached its maximum adsorption capacity of 633.92 mg/g in the short time of 15 min. The Pen G adsorption of p(GMA)-IDA-Cu²⁺ was three times more than that of the p(GMA) nanoparticles and two times more than that of the ampicillin adsorption. In addition, there was no significant decrease in the adsorption capacity of Pen G resulting from the repeated adsorption-desorption process of metal-chelated nanoparticles over five cycles. The metal-chelated nanoparticle had an 84.5% ability to regain its ability to regenerate the product with its regeneration capability, making the widespread use of the system very convenient in terms of reducing cost, an important factor in removal processes.

Fluorescence-Based Portable Assays for Detection of Biological and Chemical Analytes

Fluorescence-based detection techniques are part of an ever-expanding field and are widely used in biomedical and environmental research as a biosensing tool. These techniques have high sensitivity, selectivity, and a short response time, making them a valuable tool for developing bio-chemical assays. The endpoint of these assays is defined by changes in fluorescence signal, in terms of its intensity, lifetime, and/or shift in spectrum, which is monitored using readout devices such as microscopes, fluorometers, and cytometers. However, these devices are often bulky, expensive, and require supervision to operate, which makes them inaccessible in resource-limited settings. To address these issues, significant effort has been directed towards integrating fluorescence-based assays into miniature platforms based on papers, hydrogels, and microfluidic devices, and to couple these assays with portable readout devices like smartphones and wearable optical sensors, thereby enabling point-of-care detection of bio-chemical analytes. This review highlights some of the recently developed portable fluorescence-based assays by discussing the design of fluorescent sensor molecules, their sensing strategy, and the fabrication of point-of-care devices.

Estrogenic flavonoids and their molecular mechanisms of action

Flavonoids are a major group of phytoestrogens associated with physiological effects, and ecological and social impacts. Although the estrogenic activity of flavonoids was reported by researchers in the fields of medical, environmental and food studies, their molecular mechanisms of action have not been comprehensively reviewed. The estrogenic activity of the respective classes of flavonoids, anthocyanidins/anthocyanins, 2-arylbenzofurans/3-arylcoumarins/α-methyldeoxybenzoins, aurones/chalcones/dihydrochalcones, coumaronochromones, coumestans, flavans/flavan-3-ols/flavan-4-ols, flavanones/dihydroflavonols, flavones/flavonols, homoisoflavonoids, isoflavans, isoflavanones, isoflavenes, isoflavones, neoflavonoids, oligoflavonoids, pterocarpans/pterocarpenes, and rotenone/rotenoids, was summarized through a comprehensive literature search, and their structure-activity relationship, biological activities, signaling pathways, and applications were discussed. Although the respective classes of flavonoids contained at least one chemical mimicking estrogen, the mechanisms varied, such as those with estrogenic, anti-estrogenic, non-estrogenic, and biphasic activities, and additional activities through crosstalk/bypassing, which exert biological activities through cell signaling pathways. Such mechanistic variations of estrogen action are not limited to flavonoids and are observed among other broad categories of chemicals, thus this group of chemicals can be termed as the "estrogenome". This review article focuses on the connection of estrogen action mainly between the outer and the inner environments, which represent variations of chemicals and biological activities/signaling pathways, respectively, and form the basis to understand their applications. The applications of chemicals will markedly progress due to emerging technologies, such as artificial intelligence for precision medicine, which is also true of the study of the estrogenome including estrogenic flavonoids.

Rapid Onsite Visual Detection of Orf Virus Using a Recombinase-Aided Amplification Assay

Orf is an important zoonotic disease caused by the Orf virus (ORFV) which can cause contagious pustular dermatitis in goats and sheep. Orf is widespread in most sheep-raising countries in the world, causing huge economic losses. Although diagnostic methods for ORFV infection already exist, it is still necessary to develop a time-saving, labor-saving, specific, low-cost and visual diagnostic method for rapid detection of ORFV in the field and application in grassroots laboratories. This study establishes a DNA extraction-free, real-time, visual recombinase-aided amplification (RAA) method for the rapid detection of ORFV. This method is specific to ORFV and does not cross-react with other common DNA viruses. The detection limits of the real-time RAA and visual judgment of the RAA assay at 95% probability were 13 and 21 copies per reaction for ORFV, respectively. Compared with qPCR, the sensitivity and specificity of the real-time RAA assay were 100%, and those of the visual RAA assay were 92.31% and 100.0%, respectively. The DNA extraction-free visual detection method of RAA established in this study can meet the needs of rapid onsite detection and grassroots laboratories and has important reference value and significance for the early diagnosis of diseased animals.

Progress in Fluorescence Biosensing and Food Safety towards Point-of-Detection (PoD) System

The detection of pathogens in food substances is of crucial concern for public health and for the safety of the natural environment. Nanomaterials, with their high sensitivity and selectivity have an edge over conventional organic dyes in fluorescent-based detection methods. Advances in microfluidic technology in biosensors have taken place to meet the user criteria of sensitive, inexpensive, user-friendly, and quick detection. In this review, we have summarized the use of fluorescence-based nanomaterials and the latest research approaches towards integrated biosensors, including microsystems containing fluorescence-based detection, various model systems with nano materials, DNA probes, and antibodies. Paper-based lateral-flow test strips and microchips as well as the most-used trapping components are also reviewed, and the possibility of their performance in portable devices evaluated. We also present a current market-available portable system which was developed for food screening and highlight the future direction for the development of fluorescence-based systems for on-site detection and stratification of common foodborne pathogens.

Mn2+ modified black phosphorus nanosheets with enhanced DNA adsorption and affinity for robust sensing

To develop various biosensors, several 2D nanomaterials adsorb DNA probes (aptamers) via π-π stacking interactions. However, interference from DNA displacement by external non-targeted ligands has precluded their practical applications for specific detection and imaging at high protein concentrations. Metal coordination is an attractive strategy for biomolecular crosslinking and functional molecular self-assembly. Herein, a robust 2D biosensor nanoplatform was developed to enhance DNA adsorption and affinity using Mn²⁺-modified black phosphorus nanosheets (BPNS@Mn²⁺) via metal coordination. The Mn²⁺ can simultaneously coordinate with the lone pair electrons (π bonds) of the BPNS and nucleotide bases to provide binding sites for DNA nucleobases on the BPNS surface, which greatly enhances the stability of the inner BPNS and improves DNA adsorption and affinity. The DNA adsorption mechanism of BPNS@Mn²⁺ was also characterized, and is extensively discussed. Without any further modification, this BPNS@Mn²⁺/DNA biosensor specifically detected single-stranded DNA (linear range: 10-200 nM, detection limit: 5.76 nM) and thrombin (linear range: 20-180 nM, detection limit: 2.39 nM) in 100 nM bovine serum albumin solution. The nonspecific ligands in the environment did not affect the detection performance of the robust biosensor. In addition, the expression levels of microRNA-21 can be imaged and analyzed in living cells using this biosensor, which is consistent with the results of the polymerase chain reaction. This study highlights the potential of metal coordination in surface modification and provides new opportunities for biomedical applications of 2D nanomaterials with superior DNA-adsorption capacity, facilitating the development of biosensor design and nucleic acid/drug delivery.

Application of Electronic Nose to Discriminate Species of Mold Strains in Synthetic Brines

The chemical composition of the brine for Spanish-style table olives plays a crucial role during the fermentation process. Traditional laboratory analysis requires a high consumption of reagents, highly qualified personnel, sophisticated equipment, long analysis times, and large amounts of samples. Analysis carried out using an electronic nose (E-nose) offers an alternative, non-destructive technique and is useful in determining alterations in brines caused by microorganisms. In the present research, nine mold strains isolated from spoiled olives were inoculated in synthetic brines to determine the effect of microbial development on sensory quality, volatile profile, and the capacity of E-nose to discriminate altered brines from the healthy ones. The brines inoculated with the mold strains presented negative attributes related to aromas of mold, wood, leather, rancidity and, organic solvents among others. The highest intensity of defect was presented by the brines inoculated with the strains Galactomyces geotricum (G.G.2); three Penicillium expansum (P.E.3, P.E.4, and P.E.20); one Penicillium glabrum (P.G.19); three Aspergillus flavus (A.F.9, A.F.18, and A.F.21); and one Fusarium solani (F.S.11). A total of 19 volatile compounds were identified by gas chromatography. Sensory analysis allowed us to classify the synthetic brines based on the degree of alteration produced by the mold strains used. Also, the E-nose data were able to discriminate the inoculated brines regardless of the intensity of the defect. These results demonstrate the capacity of the E-nose to discriminate alterations in brines produced by molds, thereby making it a useful tool to be applied during the elaboration process to detect early alterations in table olive fermentation.

The importance of method validation in herbal drug research

There are countless scientific publications on herbal drugs, but unfortunately many of them do not correctly report their chemical, biological and pharmacological aspects, including the composition and stability of the herbal/extract preparations, therefore their safety, efficacy and consistency could not be proven. For developing a modern drug from herbal drug(s), complete chemical and pharmacological characterizations of their bioactive metabolites need to be well established. Reproducible results require the development, assessment, and standardization of the chemical, biological and pharmacological methods based on the current state of the art. Therefore, all methods used in research must be properly validated before its routine applications. This present review will describe and discuss the important aspects of method validation (chemical, biological and pharmacological) in herbal drug research according to the newest current Pharmacopeia, official Guidelines and related recent publications.

Aptamers-Diagnostic and Therapeutic Solution in SARS-CoV-2

The SARS-CoV-2 virus is currently the most serious challenge to global public health. Its emergence has severely disrupted the functioning of health services and the economic and social situation worldwide. Therefore, new diagnostic and therapeutic tools are urgently needed to allow for the early detection of the SARS-CoV-2 virus and appropriate treatment, which is crucial for the effective control of the COVID-19 disease. The ideal solution seems to be the use of aptamers—short fragments of nucleic acids, DNA or RNA—that can bind selected proteins with high specificity and affinity. They can be used in methods that base the reading of the test result on fluorescence phenomena, chemiluminescence, and electrochemical changes. Exploiting the properties of aptamers will enable the introduction of rapid, sensitive, specific, and low-cost tests for the routine diagnosis of SARS-CoV-2. Aptamers are excellent candidates for the development of point-of-care diagnostic devices and are potential therapeutic tools for the treatment of COVID-19. They can effectively block coronavirus activity in multiple fields by binding viral proteins and acting as carriers of therapeutic substances. In this review, we present recent developments in the design of various types of aptasensors to detect and treat the SARS-CoV-2 infection.

A fluorescent aptasensor for the detection of Aflatoxin B1 by graphene oxide mediated quenching and release of fluorescence

Aflatoxin B1 contamination in food and agro commodities has been major concern of global food safety and trade industry. There is an urgent need to develop sensitive and on-site detection methods for aflatoxins mainly, AFB1 monitoring. In the present study, a fluorophore (Alexa Fluor 488) based aptamer biosensor was devised in combination with graphene oxide (GO) for the detection of Aflatoxin B1 (AFB1). The optimized diagnostic procedure consisted of a fluorescent modified aptamer (Ax-AFLA5) as detection probe and GO mediated quenching of the same; to the quenched system AFB1 was added resulting in subsequent release of fluorescence. The principle of GO based adsorption of ssDNA and successive desorption in the presence of target mycotoxin was utilised in development of the bioassay. In presence of target mycotoxin, the GO adsorbed ssDNA attained a structural conformation resulting in desorption and subsequent release of fluorescence. Assay parameters such as concentration of fluorescent probe, GO and incubation time were evaluated and optimized. The optical signal thus generated could determine presence of AFB1 in the given sample. Selectivity of the method with other mycotoxins was evaluated. The linear range of AFB1 from 0.2-200 ppb was assessed. Visible green fluorescence release was observed at 20 ppb under UV transilluminator and the detection limit of the developed assay was interpreted as 20 ppb of AFB1. The suitability of the assay for AFB1 quantification in groundnut and natural samples was also evaluated. Thus, the developed assay can be a field deployable, reliable and rapid alternative tool for onsite screening method of aflatoxins and other mycotoxins at field level.

Paper and thread as media for the frugal detection of urinary tract infections (UTIs)

Urinary tract infections (UTIs) make up a significant proportion of the global burden of disease in vulnerable groups and tend to substantially impair the quality of life of those affected, making timely detection of UTIs a priority for public health. However, economic and societal barriers drastically reduce accessibility of traditional lab-based testing methods for critical patient groups in low-resource areas, negatively affecting their overall healthcare outcomes. As a result, cellulose-based materials such as paper and thread have garnered significant interest among researchers as substrates for so-called frugal analytical devices which leverage the material's portability and adaptability for facile and reproducible diagnoses of UTIs. Although the field may be only in its infancy, strategies aimed at commercial penetration can appreciably increase access to more healthcare options for at-risk people. In this review, we catalogue recent advances in devices that use cellulose-based materials as the primary housing or medium for UTI detection and chart out trends in the field. We also explore different modalities employed for detection, with particular emphasis on their ability to be ported onto discreet casings such as sanitary products.

Fluorescent Immunohistochemistry

Immunofluorescence is an important immunochemical technique that utilizes fluorescence-labeled antibodies to detect specific target antigens. It is used widely in both scientific research and clinical laboratories. Immunofluorescence allows for excellent sensitivity and amplification of signal in comparison to immunohistochemistry. However, analysis of samples labeled with fluorescence-labeled antibodies has to be performed using a fluorescence microscope or other type of fluorescence imaging. There are two methods available: direct (primary) and indirect (secondary) immunofluorescence. Here, we describe the principle of immunofluorescence methods as well as the preparation of fresh-frozen and formalin-fixed, paraffin embedded tissues for both direct and indirect immunofluorescence labeling.

Nanotechnology-Based Strategies for Effective and Rapid Detection of SARS-CoV-2

The coronavirus disease 2019 (COVID-19) pandemic has gained worldwide attention and has prompted the development of innovative diagnostics, therapeutics, and vaccines to mitigate the pandemic. Diagnostic methods based on reverse transcriptase-polymerase chain reaction (RT-PCR) technology are the gold standard in the fight against COVID-19. However, this test might not be easily accessible in low-resource settings for the early detection and diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The lack of access to well-equipped clinical laboratories, requirement for the high level of technical competence, and the cost of the RT-PCR test are the major limitations. Moreover, RT-PCR is unsuitable for application at the point-of-care testing (PoCT) as it is time-consuming and lab-based. Due to emerging mutations of the virus and the burden it has placed on the health care systems, there is a growing urgency to develop sensitive, selective, and rapid diagnostic devices for COVID-19. Nanotechnology has emerged as a versatile technology in the production of reliable diagnostic tools for various diseases and offers new opportunities for the development of COVID-19 diagnostic systems. This review summarizes some of the nano-enabled diagnostic systems that were explored for the detection of SARS-CoV-2. It highlights how the unique physicochemical properties of nanoparticles were exploited in the development of novel colorimetric assays and biosensors for COVID-19 at the PoCT. The potential to improve the efficiency of the current assays, as well as the challenges associated with the development of these innovative diagnostic tools, are also discussed.

High-Pressure-Induced Sublethal Injuries of Food Pathogens-Microscopic Assessment

High Hydrostatic Pressure (HHP) technology is considered an alternative method of food preservation. Nevertheless, the current dogma is that HHP might be insufficient to preserve food lastingly against some pathogens. Incompletely damaged cells can resuscitate under favorable conditions, and they may proliferate in food during storage. This study was undertaken to characterize the extent of sublethal injuries induced by HHP (300-500 MPa) on Escherichia coli and Listeria inncua strains. The morphological changes were evaluated using microscopy methods such as Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Epifluorescence Microscopy (EFM). The overall assessment of the physiological state of tested bacteria through TEM and SEM showed that the action of pressure on the structure of the bacterial membrane was almost minor or unnoticeable, beyond the L. innocua wild-type strain. However, alterations were observed in subcellular structures such as the cytoplasm and nucleoid for both L. innocua and E. coli strains. More significant changes after the HHP of internal structures were reported in the case of wild-type strains isolated from raw juice. Extreme condensation of the cytoplasm was observed, while the outline of cells was intact. The percentage ratio between alive and injured cells in the population was assessed by fluorescent microscopy. The results of HHP-treated samples showed a heterogeneous population, and red cell aggregates were observed. The percentage ratio of live and dead cells (L/D) in the L. innocua collection strain population was higher than in the case of the wild-type strain (69%/31% and 55%/45%, respectively). In turn, E. coli populations were characterized with a similar L/D ratio. Half of the cells in the populations were distinguished as visibly fluorescing red. The results obtained in this study confirmed sublethal HHP reaction on pathogens cells.

Surface enhanced Raman scattering for the multiplexed detection of pathogenic microorganisms: towards point-of-use applications

Surface enhanced Raman scattering (SERS) is a technique that demonstrates a number of advantages for the rapid, specific and sensitive detection of pathogenic microorganisms. In this review, an overview of label-free and label-based SERS approaches, including microfluidics, nucleic acid detection and immunoassays, for the multiplexed detection of pathogenic bacteria and viruses from the last decade will be discussed, as well as their transition into promising point-of-use detection technologies in industrial and medical settings.

Advances in point-of-care testing for cardiovascular diseases

Point-of-care testing (POCT) is a specific format of diagnostic testing that is conducted without accompanying infrastructure or sophisticated instrumentation. Traditionally, such rapid sample-to-answer assays provide inferior analytical performances to their laboratory counterparts when measuring cardiac biomarkers. Hence, their potentially broad applicability is somewhat bound by their inability to detect clinically relevant concentrations of cardiac troponin (cTn) in the early stages of myocardial injury. However, the continuous refinement of biorecognition elements, the optimization of detection techniques, and the fabrication of tailored fluid handling systems to manage the sensing process has stimulated the production of commercial assays that can support accelerated diagnostic pathways. This review will present the latest commercial POC assays and examine their impact on clinical decision-making. The individual elements that constitute POC assays will be explored, with an emphasis on aspects that contribute to economically feasible and highly sensitive assays. Furthermore, the prospect of POCT imparting a greater influence on early interventions for medium to high-risk individuals and the potential to re-shape the paradigm of cardiovascular risk assessments will be discussed.

SERS-Based Aptasensor for Rapid Quantitative Detection of SARS-CoV-2

During the COVID-19 pandemic, the development of sensitive and rapid techniques for detection of viruses have become vital. Surface-enhanced Raman scattering (SERS) is an appropriate tool for new techniques due to its high sensitivity. SERS materials modified with short-structured oligonucleotides (DNA aptamers) provide specificity for SERS biosensors. Existing SERS-based aptasensors for rapid virus detection are either inapplicable for quantitative determination or have sophisticated and expensive construction and implementation. In this paper, we provide a SERS-aptasensor based on colloidal solutions which combines rapidity and specificity in quantitative determination of SARS-CoV-2 virus, discriminating it from the other respiratory viruses.

Development of Two-Dimensional Nanomaterials Based Electrochemical Biosensors on Enhancing the Analysis of Food Toxicants

In recent times, food safety has become a topic of debate as the foodborne diseases triggered by chemical and biological contaminants affect human health and the food industry's profits. Though conventional analytical instrumentation-based food sensors are available, the consumers did not appreciate them because of the drawbacks of complexity, greater number of analysis steps, expensive enzymes, and lack of portability. Hence, designing easy-to-use tests for the rapid analysis of food contaminants has become essential in the food industry. Under this context, electrochemical biosensors have received attention among researchers as they bear the advantages of operational simplicity, portability, stability, easy miniaturization, and low cost. Two-dimensional (2D) nanomaterials have a larger surface area to volume compared to other dimensional nanomaterials. Hence, researchers nowadays are inclined to develop 2D nanomaterials-based electrochemical biosensors to significantly improve the sensor's sensitivity, selectivity, and reproducibility while measuring the food toxicants. In the present review, we compile the contribution of 2D nanomaterials in electrochemical biosensors to test the food toxicants and discuss the future directions in the field. Further, we describe the types of food toxicity, methodologies quantifying food analytes, how the electrochemical food sensor works, and the general biomedical properties of 2D nanomaterials.

Pathogenic Escherichia coli (E. coli) detection through tuned nanoparticles enhancement study

OBJECTIVE

This study aims to detect pathogenic Escherichia coli (E. coli) bacteria using non-destructive fluorescence microscopy and micro-Raman spectroscopy.

RESULTS

Raman vibrational spectroscopy provides additional information regarding biochemical changes at the cellular level. We have used two nanomaterials zinc oxide nanoparticles (ZnO-NPs) and gold nanoparticles (Au-NPs) to detect pathogenic E. coli. The scanning electron microscope (SEM) with energy dispersive X-ray (EDAX) spectroscopy exhibit surface morphology and the elemental composition of the synthesized NPs. The metal NPs are useful contrast agents due to the surface plasmon resonance (SPR) to detect the signal intensity and hence the bacterial cells. The changes due to the interaction between cells and NPs are further correlated to the change in the surface charge and stiffness of the cell surface with the help of the fluorescence microscopic assay.

CONCLUSIONS

We conclude that when two E. coli strains (MTCC723 and MTCC443) and NPs are respectively mixed and kept overnight, the growth of bacteria are inhibited by ZnO-NPs due to changes in cell membrane permeability and intracellular metabolic system under fluorescence microscopy. However, SPR possessed Au-NPs result in enhanced fluorescence of both pathogens. In addition, with the help of Raman microscopy and element analysis, significant changes are observed when Au-NPs are added with the two strains as compared to ZnO-NPs due to protein, lipid and DNA/RNA induced conformational changes.

Immunoassays Based on Hot Electron-Induced Electrochemiluminescence at Disposable Cell Chips with Printed Electrodes

Novel hot electron-emitting working electrodes and conventional counter electrodes were created by screen printing. Thus, low-cost disposable electrode chips for bioaffinity assays were produced to replace our older expensive electrode chips manufactured by manufacturing techniques of electronics from silicon or on glass chips. The present chips were created by printing as follows: (i) silver lines provided the electronic contacts, counter electrode and the bottom of the working electrode and counter electrode, (ii) the composite layer was printed on appropriate parts of the silver layer, and (iii) finally a hydrophobic ring was added to produce the electrochemical cell boundaries. The applicability of these electrode chips in bioaffinity assays was demonstrated by an immunoassay of human C-reactive protein (i) using Tb(III) chelate label displaying long-lived hot electron-induced electrochemiluminescence (HECL) and (ii) now for the first time fluorescein isothiocyanate (FITC) was utilized as an a low-cost organic label displaying a short-lived HECL in a real-world bioaffinity assay.

DNA microarray analysis using a smartphone to detect the BRCA-1 gene

DNA microarrays are used to examine changes in gene expression of a large number of genes simultaneously by fluorescent labeling of complementary DNAs (cDNAs). The major bottleneck in implementing microarray technology in resource-limited settings lies in the detection instrument used for generating images of spotted oligonucleotides post-hybridization. While various methods such as a lateral flow assay have been presented to accomplish point-of-care disease detection, there is no simple and effective instrument available to gather spot images maintaining the standard microarray procedures. Nanotechnology based sensors connected with a portable smartphone readout system have the potential to be implemented in microarray technology. Here, we describe a portable fluorescence microarray based imaging system connected to a smartphone for detecting breast cancer gene expression (BRCA-1) from exon 11. This is based on the interactive binding of probe DNA to Cy3-target DNA. A paper-based microfluidics approach was used to demonstrate the DNA hybridization assay. The imaging principles of the assembled device named "FluoroZen" are similar to those of a fluorescence microscope. It uses two light spectrum filters, one to excite the fluorescent dye and the other to capture the emission spectrum. The images were acquired by using CCD cameras from FluoroZen. The smartphone integrated paper microfluidics platform presented here could be translated into clinical settings to perform point-of-care testing.

An Anticaffeine Antibody-Oligonucleotide Conjugate for DNA-Directed Immobilization in Environmental Immunoarrays

The development of fast and cheap high-throughput platforms for the detection of environmental contaminants is of particular importance to understand the human-related impact on the environment. The application of DNA-directed immobilization (DDI) of IgG molecules is currently limited to the clinical diagnostics scenario, possibly because of the high costs of production of such addressable platforms. We here describe the efficient and specific hybridization of an antibody-oligonucleotide conjugate to a short 12-mer capture probe. The specific antibody used is a monoclonal antibody against caffeine, a stimulant and important anthropogenic marker. With this work, we hope to contribute to broadening the application potential of DDI to environmental markers in order to develop cheaper and more stable high-throughput screening platforms for standard routine analysis of pollutants in a variety of complex matrices.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

Development of a Magnetic Nanoparticles-Based Screen-Printed Electrodes (MNPs-SPEs) Biosensor for the Quantification of Ochratoxin A in Cereal and Feed Samples

A rapid and sensitive electrochemical biosensor based on magnetic nanoparticles and screen-printed electrodes (MNPs-SPEs sensor) was developed for the detection of ochratoxin A (OTA) in cereal and feed samples. Different types of magnetic nanoparticles-based ELISA (MNPs-ELISA) were optimized, and the signal detection, as well as sensitivity, was enhanced by the combined use of screen-printed electrodes (SPEs). Under the optimized conditions, the calibration curve of the MNPs-SPEs sensor was y = 0.3372x + 0.8324 (R² = 0.9805). The linear range of detection and the detection limit were 0.01–0.82 ng/mL and 0.007 ng/mL, respectively. In addition, 50% inhibition (IC50) was detectable at 0.10 ng/mL. The limit of detection (LOD) of this MNPs-SPEs sensor in cereal and feed samples was 0.28 μg/kg. The recovery rates in spiked samples were between 78.7% and 113.5%, and the relative standard deviations (RSDs) were 3.6–9.8%, with the coefficient of variation lower than 15%. Parallel analysis of commercial samples (corn, wheat, and feedstuff) showed a good correlation between MNPs-SPEs sensor and liquid chromatography tandem mass spectrometry (LC/MS-MS). This new method provides a rapid, highly sensitive, and less time-consuming method to determine levels of ochratoxin A in cereal and feedstuff samples.

A Fluorescent Sensor Array Based on Heteroatomic Macrocyclic Fluorophores for the Detection of Polluting Species in Natural Water Samples

The development of a novel all-solid-state optical sensor array based on heteroatomic macrocyclic fluorophores (diaza-crown ether, metallocorrole and pyridinophans) for the photographic analysis of liquid media, is presented. The sensitivity of the new optical system toward a number of different species (cations: Li⁺, K⁺, Na⁺, NH4+, Mg²⁺, Ca²⁺, Co²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺ and anions: NO2-, NO3-, Cl⁻, Br⁻, HCO3-) was evaluated both in single selective sensor mode and in multisensory arrangement. The satisfactory PLS1 regression models between sensor array optical response and analyte concentration were obtained for Cd²⁺, Cu²⁺, Zn²⁺, and NO2- ions in all the range of tested concentrations. Among these species the highest attention was focused onto detection of cadmium and nitrite ions, for which the detection limits, DL, estimated by 3σ method were found 0.0013 mg/L and 0.21 mg/L respectively, and these values are lower than the corresponding WHO guideline values of 0.003 mg/L (Cd²⁺) and 2 mg/L (NO2-). The suitability of the developed sensors implemented with familiar devices for signal acquisition (Light Emitting Diode, LED, as light source and a digital camera as a signal detector), and chemometric methods for data treatment to perform fast and low-cost monitoring of species under interest, in real samples of environmental importance, is demonstrated.

Pesticide binding and urea-induced controlled release applications with calixarene naphthalimide molecules by host-guest complexation

Three novel calix[4]arene molecule-based 1,8 naphthalimide fluoroionophore for the selective determination of kesoxim-methyl were synthesized and used in pesticide binding studies. The possible interaction between pesticides and fluorescent calix[4]arene molecules was monitored by UV/Vis absorption and fluorescence spectroscopy. When compared the studied pesticides, kesoxim-methyl was strongly quenched the fluorescence intensity of upper rim-modified calix[4]arene. UV and fluorescence titration experiments were also studied to determine both the quenching mechanism and stoichiometric ratio consisted in complex formation. Furthermore, pesticide release experiments were also performed with a fertilizing agent as urea by using fluorescence spectroscopy technique.

Sensitive multiplex detection of whole bacteria using self-assembled cell binding domain complexes

Detecting bacterial cells at low levels is critical in public health, the food industry and first response. Current processes typically involve laborious cell lysis and genomic DNA extraction to achieve 100-1000 CFU mL^-1 levels for detecting gram-positive bacteria. As an alternative to DNA-based methods, cell wall binding domains (CBDs) derived from lysins having a modular structure with an N-terminal catalytic domain and a C-terminal CBD, can be used to detect bacterial pathogens as a result of their exceptionally specific binding to target bacteria with great avidity. We have developed a highly sensitive method for multiplex detection of whole bacterial cells using self-assembled CBD complexes. Self-assembled CBD-SA-reporter complexes were generated using streptavidin (SA), biotin-CBDs, and biotinylated reporters, such as glucose oxidase (GOx) and specific DNA sequences. The simultaneous detection of three test bacteria, Staphylococcus aureus, Bacillus anthracis-Sterne, and Listeria innocua cells in PBS could be accomplished with a 96-well plate-based sandwich method using CBD-SA-GOx complex-coupled spectrophotometric assay to achieve a detection limit of >100 CFU mL^-1. To achieve greater detection sensitivity, we used CBD-SA-DNA complexes and qPCR of specific DNA barcodes selectively bound to the surface of target bacterial cells, which resulted in a detection sensitivity as low as 1-10 CFU mL^-1 without cross-reactivity. This sensitive multiplex detection of bacterial pathogens using both CBD-SA-GOx and CBD-SA-DNA complexes has the potential to be quickly combined with point-of-care compatible diagnostics for the rapid detection of pathogens in test samples.

An Electronic Nose for Royal Delicious Apple Quality Assessment - A Tri-layer Approach

Foodborne pathogens cause serious health issues and have a strong impact on the economy of the country. In this context, quality testing of royal delicious apple by detecting pathogen contamination using an electronic nose, which contains an array of six ready-made sensors, has been proposed. To estimate the types of pathogens, fresh, half and completely contaminated apple samples were considered for bacterial studies. This study revealed the presence of Staphylococcus, Salmonella and Shigella bacteria, which were in the order of zero, 10², 10³-10⁴ CFU/mL. Further, the recorded headspace GC-MS spectra of contaminated samples confirmed the presence of bacterial spoilage markers namely acetone, ethyl acetate, ethyl alcohol and acetaldehyde. Voltage swing of 0.2 and 0.5 V was observed for half and completely contaminated apple samples respectively with reference to the fresh sample. Voltage responses of the sensors fed to Principal component analysis and Ward's method of hierarchical cluster algorithms helped to assess the quality of apple samples. By correlating the results of tri-layers namely bacterial count, GCMS data and classification results, reference table was developed and embedded in the ATmega processor of the electronic nose for real-time quality estimation of apple samples.

Development and validation of a bioassay to evaluate binding of adalimumab to cell membrane-anchored TNFα using flow cytometry detection

Physicochemical and structural properties of proteins used as active pharmaceutical ingredients of biopharmaceuticals are determinant to carry out their biological activity. In this regard, the assays intended to evaluate functionality of biopharmaceuticals provide confirmatory evidence that they contain the appropriate physicochemical properties and structural conformation. The validation of the methodologies used for the assessment of critical quality attributes of biopharmaceuticals is a key requirement for manufacturing under GMP environments. Herein we present the development and validation of a flow cytometry-based methodology for the evaluation of adalimumab's affinity towards membrane-bound TNFα (mTNFα) on recombinant CHO cells. This in vitro methodology measures the interaction between an in-solution antibody and its target molecule onto the cell surface through a fluorescent signal. The characteristics evaluated during the validation exercise showed that this methodology is suitable for its intended purpose. The assay demonstrated to be accurate (r² = 0.92, slope = 1.20), precise (%CV ≤ 18.31) and specific (curve fitting, r² = 0.986-0.997) to evaluate binding of adalimumab to mTNFα. The results obtained here provide evidence that detection by flow cytometry is a viable alternative for bioassays used in the pharmaceutical industry. In addition, this methodology could be standardized for the evaluation of other biomolecules acting through the same mechanism of action.

Plant Pest Detection Using an Artificial Nose System: A Review

This paper reviews artificial intelligent noses (or electronic noses) as a fast and noninvasive approach for the diagnosis of insects and diseases that attack vegetables and fruit trees. The particular focus is on bacterial, fungal, and viral infections, and insect damage. Volatile organic compounds (VOCs) emitted from plants, which provide functional information about the plant's growth, defense, and health status, allow for the possibility of using noninvasive detection to monitor plants status. Electronic noses are comprised of a sensor array, signal conditioning circuit, and pattern recognition algorithms. Compared with traditional gas chromatography-mass spectrometry (GC-MS) techniques, electronic noses are noninvasive and can be a rapid, cost-effective option for several applications. However, using electronic noses for plant pest diagnosis is still in its early stages, and there are challenges regarding sensor performance, sampling and detection in open areas, and scaling up measurements. This review paper introduces each element of electronic nose systems, especially commonly used sensors and pattern recognition methods, along with their advantages and limitations. It includes a comprehensive comparison and summary of applications, possible challenges, and potential improvements of electronic nose systems for different plant pest diagnoses.

Estrogenic Potentials of Traditional Chinese Medicine

Estrogen, a steroid hormone, is associated with several human activities, including environmental, industrial, agricultural, pharmaceutical and medical fields. In this review paper, estrogenic activity associated with traditional Chinese medicines (TCMs) is discussed first by focusing on the assays needed to detect estrogenic activity (animal test, cell assay, ligand-binding assay, protein assay, reporter-gene assay, transcription assay and yeast two-hybrid assay), and then, their sources, the nature of activities (estrogenic or anti-estrogenic, or other types), and pathways/functions, along with the assay used to detect the activity, which is followed by a summary of effective chemicals found in or associated with TCM. Applications of estrogens in TCM are then discussed by a comprehensive search of the literature, which include basic study/pathway analysis, cell functions, diseases/symptoms and medicine/supplements. Discrepancies and conflicting cases about estrogenicity of TCM among assays or between TCM and their effective chemicals, are focused on to enlarge estrogenic potentials of TCM by referring to omic knowledge such as transcriptome, proteome, glycome, chemome, cellome, ligandome, interactome and effectome.

High-performance magnetic chicken bone-based biochar for efficient removal of rhodamine-B dye and tetracycline: competitive sorption analysis

Magnetic chicken bone-based biochar (MCBB) was successfully prepared and efficiently adsorbed rhodamine-B (RB) dye and tetracycline (TC) in multi-component systems. The magnetisation value, surface area, and pH_pzc of the MCBB were found to be 66.5 emu/g, 328 m²/g, and 8.3, respectively. RB has higher saturation capacity (96.5 mg/g) and occupies more active sites on MCBB, thus limiting the sorption of TC with lower saturation capacity (63.3 mg/g). Langmuir isotherm suitably describes the sorption process in a single-component system; however, the multi-component system was well fitted to the Sheindorf-Rebhun-Sheintuch model. The selectivity factor values confirmed that MCBB had higher adsorption affinity toward RB than TC. The intraparticle diffusion model played a significant role in the sorption process. The MCBB can be easily desorbed with base-spiked H₂O and reused without loss in stability or structural integrity.