An Aflatoxin-M1 biochip using graphene quantum dot-gold hybrid nanoparticles.

Toxicosis through food and feed has remained a point of concern to food sectors across the globe. Although strict regulations have been implemented in developed and developing countries, their detection in food matrices is an evolving science. This study focuses on the development and fabrication of an electrochemical microfluidic biosensor that deploys aptamers to detect trace concentrations of Aflatoxin-M1 (AF-M1) in milk samples. The use of graphene quantum dot composite with Au nanoparticles anchors the aptamer to the sensor surface and improves its signal conductivity. The screen-printed carbon electrode modified with graphene quantum dot-gold nanoparticles is placed between two polydimethylsiloxane layers to promote portability and improve mixing effects. Differential pulse voltammograms indicated that the linear range of the sensor was between 100 pM and 2 nM making the limit of detection 0.3 nM. Interfering molecules of similar size were analyzed, to evaluate sensor selectivity.

A review of nanoparticle synthesis and application in the suppression of diseases in fruits and vegetables.

Fruits and vegetables are an integral part of our diet attributed to their appealing taste, flavor, and health-promoting characteristics. However, due to their high-water activity, they are susceptible to microbial spoilage and diseases at any step in the food supply chain, from pre-harvest treatment to post-harvest storage and transportation. As a result, food researchers and engineers are developing innovative technologies that can be used to reduce the loss of fruits and vegetables on-farm and during postharvest processing. The purpose of this study was to gather and discuss the scientific data on the disease-suppressive activity of nanoparticles against plant pathogens. The progress and limitations of innovative approaches for improving nanoparticles' efficiency and dependability have been studied to develop effective substitutes for synthetic chemical fungicides and pesticides, in managing disease in fruits and vegetables. The findings of this study strongly suggests that nanotechnology has the required ability for disease suppression in fruits and vegetables. Applications of specific nanoparticles under specified conditions can enhance nutrition delivery to plants, provide better antibacterial and disease suppression activity. Nanoparticles can also lessen the quantity of agrichemicals/metals released into the environment as compared to standard formulations, which is one of the most impressive advances.

A reusable QCR aptasensor for the detection of Brevetoxin-2 in shellfish.

Brevetoxins (BTX) are pharmacologically active, lipid soluble cyclic polyether neurotoxins that are known to cause a wide range of neurological symptoms in humans.Harvesting and consumption of infected molluscs provide an entry point for BTXs into, the food chain, causing long-term health effects on accumulation for individuals, commonly in people with a compromised immune system and existing allergies. This study is an acoustic assay that has been constructed using a 9 MHz AT-cut quartz crystal resonator modified by attaching a specific single-stranded DNA aptamer. The DNA oligo modifies its conformation to attach itself to the binding site of the incoming BTX molecule resulting in a change in frequency on the QCR. A small Δf value was observed for lower concentrations of BTX indicating a small change in mass deposited on the crystal surface, while the opposite was true for higher concentrations. Cross-species behavior was evaluated using samples of similar origin, molecular weight and a combination of two toxins. The LOD of the fabricated QCR is 220 nM which is lower than the maximum recommended residue limit in food samples. Fresh mussel samples were spiked with known concentrations of BTX to evaluate its sensitivity in a food matrix. No interaction with other compounds was observed. Overall, this sensor finds potential application in the food sector (fishing units) where mussels are tested and graded for allergens and toxins before reaching the customer.

A Paper-Based Colorimetric Aptasensor for the Detection of Gentamicin.

Antibiotics are classes of antimicrobial substances that are administered widely in the field of veterinary science to promote animal health and feed efficiency. Cattle-administered antibiotics hold a risk of passing active residues to milk, during the milking process. This becomes a public health concern as these residues can cause severe allergic reactions to sensitive groups and considerable economic losses to the farmer. Hence, to ensure that the produced milk is safe to consume and adheres to permissible limits, an on-farm quick and reliable test is essential. This study illustrates the design and development of a microfluidic paper biosensor as a proof-of-concept detection system for gentamicin in milk. Localized surface plasmon resonance (LSPR) properties of gold nanoparticles have been explored to provide the user a visual feedback on the test, which was also corroborated by RGB analysis performed using Image J. The assay involves the use of a short stretch of single stranded DNA, called aptamer, which is very specific to the gentamicin present in the milk sample. The camera-based LOD for the fabricated paper device for milk samples spiked with gentamicin was calculated to be 300 nM, with a reaction time of 2 min.

An electrochemical microfluidic biochip for the detection of gliadin using MoS2/graphene/gold nanocomposite.

Testing gluten content in food, before it reaches the consumer, becomes a major challenge where cross-contamination during processing and transportation is a very common occurrence. In this study, a microfluidic electrochemical aptasensing system for the detection of gliadin has been proposed. The fabrication of the sensor involves its modification by using a combination of 2D nanomaterial molybdenum disulfide (MoS2)/graphene with the addition of gold (Au) nanoparticles. Aptamers, a short string of nucleotide bases that are very specific to gliadin, were used in this sensor as the biomarker. The electrochemical standard reduction potential of the ferro-ferricyanide indicator was found to be ~ 530 mV. This setup was integrated with a unique polydimethylsiloxane (PDMS)-based flexible microfluidic device for sample enrichment and portability. The results of this sensor show that the limit of detection was 7 pM. The total sample assay time was 20 min and a good linear range was observed from 4 to 250 nM with an R2 value of 0.982. Different flour samples sourced from the local market were tested and interfering molecules were added to ensure selectivity. The study shows promise in its applicability in real-time gliadin detection.Graphical abstract.

Characterisation of graphene electrodes for microsystems and microfluidic devices.

Fabrication of microsystems is traditionally achieved with photolithography. However, this fabrication technique can be expensive and non-ideal for integration with microfluidic systems. As such, graphene fabrication is explored as an alternative. This graphene fabrication can be achieved with graphite oxide undergoing optical exposure, using optical disc drives, to impose specified patterns and convert to graphene. This work characterises such a graphene fabrication, and provides fabrication, electrical, microfluidic, and scanning electron microscopy (SEM) characterisations. In the fabrication characterisation, a comparison is performed between traditional photolithography fabrication and the new graphene fabrication. (Graphene fabrication details are also provided.) Here, the minimum achievable feature size is identified and graphene fabrication is found to compare favourably with traditional photolithography fabrication. In the electrical characterisation, the resistivity of graphene is measured as a function of fabrication dose in the optical disc drive and saturation effects are noted. In the microfluidic characterisation, the wetting properties of graphene are shown through an investigation of the contact angle of a microdroplet positioned on a surface that is treated with varying fabrication dose. In the SEM characterisation, the observed effects in the previous characterisations are attributed to chemical or physical effects through measurement of SEM energy dispersive X-ray spectra and SEM images, respectively. Overall, graphene fabrication is revealed to be a viable option for development of microsystems and microfluidics.

Phosphorene-gold nanocomposite based microfluidic aptasensor for the detection of okadaic acid.

Okadaic acid (OA) is one of the most prevalent and largely distributed bio-toxin in the world. Consumption of OA results in a series of digestive ailments such as nausea and diarrhea. This study demonstrates the preparation and functioning of an electrochemical microfluidic biochip for the detection of OA. The screen-printed carbon electrode (SPCE) was modified by phosphorene-gold nanocomposite onto which an aptamer specific to OA was immobilized. BP-Au nanocomposites were synthesized by an in-situ, one-step method without the use of a reducing agent. Potassium ferro-ferri cyanide was used as a redox pair to quantify signal strength. To improve reaction time, increase sensitivity and portability, a microfluidic platform was designed and developed. This device comprised of channels identified for specific purposes such as sample mixing and incubation. Overall, the integrated system consisted of a polydimethylsiloxane microfluidic chip housing an aptamer modified SPCE, as a single detection module for Okadaic acid. The nanomaterials and the microfluidic channels prepared were spectroscopically and electrochemically analyzed. Differential pulse voltammograms revealed a detection limit of 8 pM, while a linear range was found between 10 nM-250 nM. Selectivity studies were also performed with spiked mussel samples and other interfering species. This point-of-care device can be deployed to perform on-farm assays in fishing units.

A 2D transition-metal dichalcogenide MoS2 based novel nanocomposite and nanocarrier for multiplex miRNA detection.

Nanoscale MoS2 has attracted extensive attention for sensing due to its superior properties. This study outlines a microfluidic and electrochemical biosensing methodology for the multiplex detection of paratuberculosis-specific miRNAs. Herein, we report the synthesis of MoS2 nanosheets decorated with a copper ferrite (CuFe2O4) nanoparticle composite and molecular probe immobilized MoS2 nanosheets as nanocarriers for the electrochemical detection of miRNAs. Paratuberculosis is a bacterial infection of the intestinal tract of dairy cattle, and is a cause of substantial economic and animal losses all over the world. The designed biosensing electrode was modified with the synthesized MoS2-CuFe2O4 nanocomposites for a highly amplified signal generation. Additionally, selective detection of miRNAs was accomplished by functionalizing the MoS2 nanosheets with a miRNA-specific biotin-tagged thiolated molecular probe and ferrocene thiol. The presence of target miRNA triggered the opening of the molecular probe present on the nanocarriers. The interaction of the molecular probe and miRNA resulted in an increase in the electrochemical signal from ferrocene. The optimized microfluidic biosensor was employed to detect a range of miRNA concentrations from the target analyte. Using square wave voltammetric analysis, a detection limit of 0.48 pM was calculated, with a detection range of 1 pM to 1.5 nM. The application of the biosensor was also assessed by detecting miRNAs in spiked serum and positive clinical samples. The developed nanomaterial enabled biosensor easily discriminated between the target miRNAs and other interfering molecules. The developed microfluidic biosensor has the potential to be used as a point-of-care, miRNA based diagnostic tool for paratuberculosis in dairy cows.