Paper-based microfluidic device for bisphenol A based chemical reaction and image analysis

A wax chalk and self-heating paper-based analytical device (SH-PAD) for the detection of bisphenol A

Bisphenol A (BPA) is a synthetic xenoestrogen widely present in the environment, known for its toxicity, endocrine-disrupting nature, carcinogenicity, and mutagenic effects on living organisms. The detection of BPA is essential as it infiltrates the human body through food, water, dust and dermal contact. Conventional methods currently in use are inadequate for on-the-spot detection. Consequently, there is a pressing need to build an all-in-one device that can be quickly fabricated using readily available and cost-effective off-the-shelf materials for the detection of BPA. Firstly, we have leveraged wax chalk for fabricating hydrophobic barriers on paper, which offers a hydrophilic channel resolution of 1.64 mm ± 0.05 mm and also the ability to confine major aqueous solvents without leakage. The fabricated device was used to detect BPA using the Folin-Ciocalteu reagent and sodium carbonate (in the presence of heat). Secondly, we have developed a self-heating paper-based analytical device (SH-PAD) using masking tape, lamination paper and Whatman filter paper. This cost-effective approach (0.017$) is based on an exothermic reaction caused by sodium hydroxide and a small quantity of aluminium in the paper layers and can retain heat adequately for more than 5 minutes, addressing the challenge of external heat sources and enabling effective and rapid colorimetric detection of BPA using the Folin-Ciocalteu reagent and sodium carbonate. Both methods can detect up to 2 μg mL-1 in spiked water samples. This developed method's user-friendliness and cost-effectiveness make it a promising candidate for point-of-care diagnostics or detection, providing testing capabilities in areas with limited resources.

MXene-reinforced octahedral PtCu nanocages with boosted electrocatalytic performance towards endocrine disrupting pollutants sensing

Rational tailoring of hollow and porous bimetallic structures with excellent electrocatalytic performance is appealing yet challenging. Further, combining independent bimetallic nanoparticles with flexible two-dimensional substrate by forming stable heterocomplex is still highly desired for electrocatalysis. Herein, hierarchical PtCu alloy octahedrons with hollow interiors and nanosheet-assembled nanoshells were synthesized by a facile and efficient chemical transformation strategy using Cu₂O as sacrificial templates. Such octahedral PtCu nanocages displayed significantly enhanced electrocatalytic activity owing to their unique hollow and porous architectures which provided easy access for analytes to the catalyst surface. Thereafter, introduction of Ti₃C₂T_x MXene was realized via simple incubation of Ti₃C₂T_x in solution containing the 3-aminopropyltriethoxysilane-capped PtCu, and their electrostatic interaction guaranteed the firm adsorption of PtCu nanocages on Ti₃C₂T_x nanosheets. It turned out that the sensitivity of the hybrid sensor was remarkably improved for electrochemical monitoring of endocrine disrupting pollutants in water, exhibiting ultrawide linear ranges and sub-nanomole detection limits. The eminent electrode performance is attributed to the high specific area, fast electrochemical kinetics, decent electrical catalytic ability, and the synergistic effect between Pt, Cu, and MXene.

A paper-analytical device for detecting bisphenol-A in foods

Bisphenol A (BPA) is a plastic monomer that can leach into food and cause adverse health effects with long-term exposure. In this study, we developed simple paper-analytical devices (PADs) for detecting BPA in food. The PADs were designed with hydrophilic and hydrophobic areas via wax printing. The hydrophilic areas were designed as a detection zone and modified with carboxymethyl cellulose (CMC) for the immobilisation of BPA-bovine serum albumin (BSA). The monoclonal antibodies against BPA were generated and modified with quantum dots (QDs) to synthesise QD-antibody (QD-Ab) probes. Detection conditions of the assay were optimized, with results of 0.1 μg of BPA-BSA and 30-fold diluted QD-Ab probes. The detection limit was 0.098 μg L^-1 using ImageJ analysis. Samples of drinking water, green tea beverage and peanut cooking oil were selected to conduct the matrix effect study. The recovery rates of BPA in different samples ranged from 78.77% to 118.96%, proving that the PADs were a simple and sensitive detection method for easy, low-cost analysis of real food samples.

Photometric Screening of Tetrabromobisphenol A in Resin Using Iron(III) Nitrate/Hexacyanoferrate(III) Mixture as a Colorimetric Reagent

This study aims to provide a simple way to identify the possibility of tetrabromobisphenol A (TBBPA) present in polymers without the need for complicated separation with expensive equipment. Since the presence of phenolic hydroxyl groups is known to be identifiable by the reduction of Fe³⁺ to Fe²⁺ in a ferric coloring reagent, the possibility of TBBPA being present in a polymer can be screened by a photometric measurement. A mixed solution of iron(III) nitrate and potassium hexacyanide(III) acid was used as a ferric coloring reagent. With this method, the concentration of TBBPA can be estimated from the photometric absorbance corresponding to the depth of the blue color produced by reduction of the ferric reagent in the presence of Fe(NO₃)₃. The limit of detection (LOD) was determined to be approximately 2 mg/kg using the Student's t-test (99% confidence), and a reproducibility of approximately 3% was determined by the relative standard deviation (RSD) from measurements of calibration samples (n = 7). Furthermore, TBBPA in actual polymer samples was screened without the need for any complex processing steps. Because this colorimetric method measures TBBPA by detecting phenolic groups, it may overestimate the TBBPA concentration in the presence of other similar phenolic substances. Nonetheless, this simple colorimetric method should help to quickly identify the presence of TBBPA in various polymers.

Eco-friendly pH detecting paper-based analytical device: Towards process intensification

This work describes the development of a miniaturized paper-based pH detection platform using natural dye extracted from red cabbage (Brassica oleracea). The easily available paper was used as a substrate and the requisite patterned zone was created with the aid of a punching machine. Experimental parameters were optimized to obtain the best signal readout. The performance of the device at different pH values was quantitatively assessed using digital image analysis with various color space models. Regression analysis suggested that a∗ parameter in CIEL∗a∗b∗ color space model, which captures the variations on the red-green scale, exhibited the best fit with experimental data (R² = 0.9754). This parameter was used for the quantitative estimation of pH variations in a wide range of pH (1-12). A series of real test samples were examined using the paper-based device and results validated with a standard pH meter. The use of paper and natural dye makes the device eco-friendly. The simplicity of fabrication, ease of usage and low reagent and sample volume requirements render the methodology suitable for in situ measurements of pH. The approach demonstrated here would pave the way for the development of clean, sustainable and intensified chemical sensor technologies.

Removal of emerging contaminants from wastewater during chemically enhanced primary sedimentation and acidogenic sludge fermentation

A novel wastewater treatment process, which couples chemically enhanced primary sedimentation (CEPS) of sewage with acidogenic fermentation of sludge in tandem, has recently been developed to improve the removal of pollutants and nutrients, and recover valuable resources such as phosphorus and organics. This study represented the first laboratory-based examination on the level and removal of the emerging contaminants, including retinoids (i.e., retinoic acids (RAs) and their metabolites) and oestrogenic endocrine disrupting chemicals (EDCs; e.g., 4-nonylphenol, bisphenol A, etc.), in sewage, sludge and its supernatant during this novel wastewater treatment process. The results showed that 65% of retinoids and 73% of EDCs were removed from sewage after aluminum (Al) based CEPS, while 80% of retinoids and 72% of EDCs were removed after iron (Fe) based CEPS. After acidogenic fermentation of the CEPS sludge, 50% and 58% of retinoids, and 50% and 47% of EDCs were further removed in the supernatants of Al-sludge and Fe-sludge, respectively. While there were comparable removals for these two classes of emerging contaminants during Al- and Fe-based CEPS and sludge fermentation, Fe-based CEPS of sewage and sludge fermentation should be preferentially considered, given the relatively lower production of Fe-sludge and lower accumulation of retinoids in Fe-sludge. The levels of retinoids and EDCs in the supernatant and sludge changed during acidogenic fermentation of Fe-sludge. The removals of at-4-oxo-RA (i.e., the dominant retinoid) and bisphenol A (i.e., the dominant EDC) in the supernatant followed the pseudo first-order reaction model, with a half-life of 1.62 days (in the first two days) and 1.55 days (in the whole experiment of seven days), respectively. The results demonstrated the effective removal of emerging contaminants from the sewage and the supernatant during the CEPS and acidogenic sludge fermentation.

A foldable isothermal amplification microdevice for fuchsin-based colorimetric detection of multiple foodborne pathogens

In this study, we have developed a foldable microdevice fully integrating DNA purification, amplification, and detection processes for detecting multiple foodborne pathogens. Specifically, the loop-mediated isothermal amplification (LAMP) technique was combined with a fuchsin-based direct DNA colorimetric detection method. The microdevice was composed of three parts: a sample zone, reaction zone, and detection zone. A sealing film attached to the sample, reaction, and detection zones served as a bottom layer to make the microdevice foldable. The detection zone was made up of paper strips attached to the sticky side of the sealing film, and fuchsin-stained lines were drawn on the paper strips. The microdevice can be folded to directly transfer the DNA template solution from the sample chambers to the reaction chambers. In this manner, fluid manipulation was readily realized and the use of a bulky instrument such as a pump or rotator was completely dispensed with. After the LAMP reaction, the detection zone was folded so that the fuchsin-stained lines were completely soaked into the reaction chambers. Genomic DNAs of Salmonella spp. and Escherichia coli O157:H7 were first successfully purified from thermally-lysed milk using polydopamine-coated paper, amplified by LAMP, and directly identified by the naked eye using fuchsin within 65 min. Using this microdevice, approximately 102 CFU per mL of Salmonella spp. was detected. These results indicate the significant potential of this microdevice for the sample-in-answer-out genetic analysis of multiple foodborne pathogens in resource-limited environments.

Quantitative screening for endocrine-disrupting bisphenol A in consumer and household products using NanoAptamer assay

The NanoAptamer assay is a bisphenol A (BPA) quantification method that uses magnetic beads, quantum dot nanoparticles, and a BPA-specific aptamer. In this study, screening of various consumer and household products for BPA was demonstrated utilizing the NanoAptamer assay. First, the experimental conditions suitable for BPA detection using the NanoAptamer assay were examined in terms of incubation time, temperature, and buffer composition. The range of BPA quantification via the NanoAptamer assay was determined to be 0.005-1000 ng/mL of BPA. The selectivity was confirmed by detecting BPA in an analog mixture containing bisphenol S and bisphenol F. Finally, a leaching experiment using 20 consumer and household products classified into 4 categories was performed to demonstrate the capability of the NanoAptamer assay for BPA detection. The experiment was validated by high-performance liquid chromatography analysis (correlation coefficient, r = 0.99).

Detection of bisphenol A using palm-size NanoAptamer analyzer

We have demonstrated a palm-size NanoAptamer analyzer capable of detecting bisphenol A (BPA) at environmentally relevant concentrations (<1ng/mL or ppb). It is designed for performing reaction and fluorescence measurement on single cuvette sample. Modified NanoGene assay was used as the sensing mechanism where signaling DNA and QD₆₅₅ was tethered to QD₅₆₅ and magnetic bead via the aptamer. Aptamer affinity with BPA resulted in the release of the signaling DNA and QD₆₅₅ from the complex and hence corresponding decrease in QD₆₅₅ fluorescence measurement signal. Baseline characterization was first performed with empty cuvettes, quantum dots and magnetic beads under near-ideal conditions to establish essential functionality of the NanoAptamer analyzer. Duration of incubation time, number of rinse cycles, and necessity of cuvette vibration were also investigated. In order to demonstrate the capability of the NanoAptamer analyzer to detect BPA, samples with BPA concentrations ranging from 0.0005 to 1.0ng/mL (ppb) were used. The performance of the NanoAptamer analyzer was further examined by using laboratory protocol and commercial spectrofluorometer as reference. Correlation between NanoAptamer analyzer and laboratory protocol as well as commercial spectrofluorometer was evaluated via correlation plots and correlation coefficients.

Inkjet-Printing Enzyme Inhibitory Assay Based on Determination of Ejection Volume

An accurate, rapid, and cost-effective methodology for enzyme inhibitor assays is highly needed for large-scale screening to evaluate the efficacy of drugs at the molecular level. For the first time, we have developed an inkjet printing-based enzyme inhibition assay for the assessment of drug activity using a conventional inkjet printer composed of four cartridges. The methodology is based on the determination of the number of moles of the drug on the printed surface. The number of moles was quantified through the volume of substance ejected onto the printed surface. The volume ejected on the reaction spot was determined from the density of reagent ink solution and its weight loss after printing. A xanthine oxidase (XOD) inhibition assay was executed to quantitatively evaluate antioxidant activities of the drug based on the determination of the number of moles of the drug ejected by inkjet printing. The assay components of xanthine, nitro blue tetrazolium (NBT), superoxide dismutase (SOD)/drug, and XOD were printed systematically on A4 paper. A gradient range of the number of moles of SOD/drug printed on A4 paper could be successfully obtained. Because of the effect of enzyme activity inhibition, incrementally reduced NBT formazan colors appeared on the paper in a number-of-moles-dependent manner. The observed inhibitory mole (IM₅₀) values of tested compounds exhibited a similar tendency in their activity order, compared to the IC₅₀ values observed through absorption assay in well plates. Inkjet printing-based IM50 assessment consumed a significantly smaller reaction volume (by 2-3 orders of magnitude) and more rapid reaction time, compared to the well-plate-based absorption assay.