Prototype Digital Lateral Flow Sensor Using Impact Electrochemistry in a Competitive Binding Assay.

This work demonstrates a lateral flow assay concept on the basis of stochastic-impact electrochemistry. To this end, we first elucidate requirements to employ silver nanoparticles as redox-active labels. Then, we present a prototype that utilizes nanoimpacts from biotinylated silver nanoparticles as readouts to detect free biotin in solution based on competitive binding. The detection is performed in a membrane-based microfluidic system, where free biotin and biotinylated particles compete for streptavidin immobilized on embedded latex beads. Excess nanoparticles are then registered downstream at an array of detection electrodes. In this way, we establish a proof of concept that serves as a blueprint for future "digital" lateral flow sensors.

Rapid detection of single E. coli bacteria using a graphene-based field-effect transistor device.

Contamination of surface and drinking water due to the presence of Escherichia coli bacteria is a major cause of water-borne disease outbreak. To address unmet challenges for practical pathogen detection in contaminated samples, we report fabrication of thermally reduced graphene oxide-based field-effect transistor (rGO FET) passivated with an ultrathin layer of Al2O3 for real-time detection of E. coli bacteria. The sensor could detect a single E. coli cell within 50 s in a 1 µL sample volume. The ultrathin layer of Al2O3 acted as a barrier between rGO and potential interferents present in the sample. E. coli specific antibodies anchored on gold nanoparticles acted as probes for selective capture of E. coli. The high density of negative charge on the surface of E. coli cells strongly modulates the concentration of majority charge carriers in the rGO monolayer, thereby allowing real-time monitoring of E. coli concentration in a given sample. With a low detection limit of single cell, the FET sensor had a linear range of 1-100 CFU in 1 µL volume of sample (i.e., 103 to 105 CFU/ mL). The biosensor with good selectivity and rapid detection was further successfully demonstrated for E. coli sensing in river water. The rGO-based FET sensor provides a low cost and label-free approach, and can be mass produced for detection of a broad spectrum of pathogens in water or other liquid media.

Can the mechanical activation (polishing) of screen-printed electrodes enhance their electroanalytical response?

The mechanical activation (polishing) of screen-printed electrodes (SPEs) is explored and shown to exhibit an improved voltammetric response (in specific cases) when polished with either commonly available alumina slurry or diamond spray. Proof-of-concept is demonstrated for the electrochemical sensing of nitrite where an increase in the voltammetric current is found using both polishing protocols, exhibiting an improved limit of detection (3σ) and a two-fold increase in the electroanalytical sensitivity compared to the respective un-polished counterpart. It is found that mechanical activation/polishing increases the C/O ratio which significantly affects inner-sphere electrochemical probes only (whereas outer-sphere systems remain unaffected). Mechanical activation/polishing has the potential to be a simple pre-treatment technique that can be extended and routinely applied towards other analytes for an observable improvement in the electroanalytical response.

Utilising copper screen-printed electrodes (CuSPE) for the electroanalytical sensing of sulfide.

A mediatorless sulfide electrochemical sensing platform utilising a novel nanocopper-oxide screen-printed electrodes (CuSPE) is reported for the first time. The state-of-the-art screen-printed electrochemical sensors demonstrate their capability to quantify sulfide within both the presence and absence of an array of interferents with good levels of sensitivity and repeatability. The direct sensing (using linear sweep voltammetry) of sulfide utilising the CuSPEs provides a mediatorless approach for the detection of sulfide, yielding useful analytical signatures that can be successfully quantified. The proposed novel protocol using the CuSPEs is successfully applied to the sensing of sulfide within drinking water exhibiting a high level of recovery.

Probing extracellular acidity of live cells in real time for cancer detection and monitoring anti-cancer drug activity.

We report a novel electrochemical strategy to probe the microenvironment of live cells in real time in terms of its extracellular pH. This approach allowed highly sensitive detection of cancer cells down to five cells. Utility of the sensor for evaluating the efficacy of glycolysis inhibiting anti-cancer drugs is also demonstrated.

Understanding psychological distress among mothers in rural Nepal: a qualitative grounded theory exploration.

BACKGROUND: There is a large burden of psychological distress in low and middle-income countries, and culturally relevant interventions must be developed to address it. This requires an understanding of how distress is experienced. We conducted a qualitative grounded theory study to understand how mothers experience and manage distress in Dhanusha, a low-resource setting in rural Nepal. We also explored how distressed mothers interact with their families and the wider community. METHODS: Participants were identified during a cluster-randomised controlled trial in which mothers were screened for psychological distress using the 12-item General Health Questionnaire (GHQ-12). We conducted 22 semi-structured interviews with distressed mothers (GHQ-12 score ≥ 5) and one with a traditional healer (dhami), as well as 12 focus group discussions with community members. Data were analysed using grounded theory methods and a model was developed to explain psychological distress in this setting. RESULTS: We found that distress was termed tension by participants and mainly described in terms of physical symptoms. Key perceived causes of distress were poor health, lack of sons, and fertility problems. Tension developed in a context of limited autonomy for women and perceived duty towards the family. Distressed mothers discussed several strategies to alleviate tension, including seeking treatment for perceived physical health problems and tension from doctors or dhamis, having repeated pregnancies until a son was delivered, manipulating social circumstances in the household, and deciding to accept their fate. Their ability to implement these strategies depended on whether they were able to negotiate with their in-laws or husbands for resources. CONCLUSIONS: Vulnerability, as a consequence of gender and social disadvantage, manifests as psychological distress among mothers in Dhanusha. Screening tools incorporating physical symptoms of tension should be envisaged, along with interventions to address gender inequity, support marital relationships, and improve access to perinatal healthcare.

Synthesis of mesostructured polyaniline using mixed surfactants, anionic sodium dodecylsulfate and non-ionic polymers and their applications in H2O2 and glucose sensing.

Mesostructured polyaniline was prepared by the self-assembly of a mixture of an anionic surfactant, sodium dodecylsulfate and a non-ionic polymeric surfactant (polyethylene glycol, and block-co-polymers such as Pluronic P123 and Brij-35). Materials were characterized by a complementary combination of X-ray diffraction, Scanning electron microscopy, Fourier-transform infrared spectrometer and UV-visible spectrophotometer. Mesostructured polyaniline was used for construction of biosensor, which displayed excellent electrocatalytic response for the detection of H(2)O(2) and glucose compared to conventional polyaniline. The electrocatalytic response observed in the case of mesostructured polyaniline can be correlated with the large surface area and nanopores which enhances the accessibility of H(2)O(2)/glucose molecule to the active site that result in high observed current. The methodology adopted in the present study provides a new platform for the fabrication of polyaniline based high-performance glucose and other biosensors.