Tyrosinase-Conjugated Prussian Blue-Modified Nickel Oxide Nanoparticles-Based Interface for Selective Detection of Dopamine

The potential of a novel enzyme-based surface plasmon resonance biosensor for direct detection of dopamine

Dopamine is one of the significant neurotransmitters and its monitoring in biological fluids is a critical issue in healthcare and modern biomedical technology. Here, we have developed a dopamine biosensor based on surface plasmon resonance (SPR). For this purpose, the carboxymethyl dextran SPR chip was used as a surface to immobilize laccase as a bioaffinity recognition element. Data analysis exhibited that the acidic pH value is the optimal condition for dopamine interaction. Calculated kinetic affinity (KD) (48,545 nM), obtained from a molecular docking study, showed strong association of dopamine with the active site of laccase. The biosensor exhibited a linearity from 0.01 to 189 μg/ml and a lower detection limit of 0.1 ng/ml (signal-to-noise ratio (S/N) = 3) that is significantly higher than the most direct dopamine detecting sensors reported so far. Experiments for specificity in the presence of compounds that can co-exist with dopamine detection such as ascorbic acid, urea and L-dopa showed no significant interference. The current dopamine biosensor with high sensitivity and specificity, represent a novel detection tool that offers a label-free, simple procedure and cost effective monitoring system.

Amplification-free electrochemical biosensor detection of circulating microRNA to identify drug-induced liver injury

Drug-induced liver injury (DILI) is a major challenge in clinical medicine and drug development. There is a need for rapid diagnostic tests, ideally at point-of-care. MicroRNA 122 (miR-122) is an early biomarker for DILI which is reported to increase in the blood before standard-of-care markers such as alanine aminotransferase activity. We developed an electrochemical biosensor for diagnosis of DILI by detecting miR-122 from clinical samples. We used electrochemical impedance spectroscopy (EIS) for direct, amplification free detection of miR-122 with screen-printed electrodes functionalised with sequence specific peptide nucleic acid (PNA) probes. We studied the probe functionalisation using atomic force microscopy and performed elemental and electrochemical characterisations. To enhance the assay performance and minimise sample volume requirements, we designed and characterised a closed-loop microfluidic system. We presented the EIS assay's specificity for wild-type miR-122 over non-complementary and single nucleotide mismatch targets. We successfully demonstrated a detection limit of 50 pM for miR-122. Assay performance could be extended to real samples; it displayed high selectivity for liver (miR-122 high) comparing to kidney (miR-122 low) derived samples extracted from murine tissue. Finally, we successfully performed an evaluation with 26 clinical samples. Using EIS, DILI patients were distinguished from healthy controls with a ROC-AUC of 0.77, a comparable performance to qPCR detection of miR-122 (ROC-AUC: 0.83). In conclusion, direct, amplification free detection of miR-122 using EIS was achievable at clinically relevant concentrations and in clinical samples. Future work will focus on realising a full sample-to-answer system which can be deployed for point-of-care testing.

Recent Advances in the Development and Characterization of Electrochemical and Electrical Biosensors for Small Molecule Neurotransmitters

Neurotransmitters act as chemical messengers, determining human physiological and psychological function, and abnormal levels of neurotransmitters are related to conditions such as Parkinson's and Alzheimer's disease. Biologically and clinically relevant concentrations of neurotransmitters are usually very low (nM), so electrochemical and electronic sensors for neurotransmitter detection play an important role in achieving sensitive and selective detection. Additionally, these sensors have the distinct advantage to potentially be wireless, miniaturized, and multichannel, providing remarkable opportunities for implantable, long-term sensing capabilities unachievable by spectroscopic or chromatographic detection methods. In this article, we will focus on advances in the development and characterization of electrochemical and electronic sensors for neurotransmitters during the last five years, identifying how the field is progressing as well as critical knowledge gaps for sensor researchers.

The Design of Ternary Composite Polyurethane Membranes with an Enhanced Photocatalytic Degradation Potential for the Removal of Anionic Dyes

Photocatalysis is an efficient and an eco-friendly way to eliminate organic pollutants from wastewater and filtration media. The major dilemma coupled with conventional membrane technology in wastewater remediation is fouling. In this study, the photocatalytic degradation potential of novel thermoplastic polyurethane (TPU) based NiO on aminated graphene oxide (NH₂-GO) nanocomposite membranes was explored. The fabrication of TPU-NiO/NH₂-GO membranes was achieved by the phase inversion method and analyzed for their performances. The membranes were effectively characterized in terms of surface morphology, functional group, and crystalline phase identification, using scanning electron microscopy, Fourier transformed infrared spectroscopy, and X-ray diffraction analysis, respectively. The prepared materials were investigated in terms of photocatalytic degradation potential against selected pollutants. Approximately 94% dye removal efficiency was observed under optimized conditions (i.e., reaction time = 180 min, pH 3-4, photocatalyst dose = 80 mg/100 mL, and oxidant dose = 10 mM). The optimized membranes possessed effective pure water flux and excellent dye rejection (approximately 94%) under 4 bar pressure. The nickel leaching in the treated wastewater sample was determined using inductively coupled plasma-optical emission spectrometry (ICP-OES). The obtained data was kinetically analyzed using first- and second-order reaction kinetic models. A first-order kinetic study was suited for the present study. Besides, the proposed membranes provided excellent photocatalytic ability up to six reusability cycles. The combination of TPU and NH₂-GO provided effective strength to membranes and the immobilization of NiO nanoparticles improved the photocatalytic behavior.

A decoupler-free simple paper microchip capillary electrophoresis device for simultaneous detection of dopamine, epinephrine and serotonin

This paper demonstrates a new and simplified configuration for capillary electrophoresis-amperometric detection (CE-AD) using a paper microfluidic chip incorporating inexpensive wax printing and screen printing based methods and then used for electrophoretic separation and simultaneous in-channel amperometric detection of three clinically relevant neurochemicals in a single run without using any decouplers. Detection of neurochemicals e.g., dopamine, epinephrine and serotonin is crucial for early prediction of neurological disorders including Parkinson's, Alzheimer's, dementia, as well as progressive neuro-psychiatric conditions such as depression, anxiety, as well as certain cardiovascular diseases. The plasma concentrations of such neurochemicals are as important as those present in cerebrospinal fluid (CSF) and can be useful for rapid and convenient biosensing. However, simultaneous detection of such neurochemicals in a complex mixture such as human serum requires their separation prior to detection. With the developed microchip, separation and detection of the neurochemicals were exhibited within 650 seconds without pre-treatment and the procedure was validated with spiked fetal bovine serum samples. Beside this, the developed paper microfluidic chip has potential to be integrated in point-of-care diagnosis with onsite detection ability. Moreover, the use of a straight channel capillary, a screen-printed carbon electrode without decoupler, in-channel amperometric detection and low sample volume requirements (2 μL) are shown as additional advantages.

This paper demonstrates a simplified configuration for capillary electrophoresis-amperometric detection using paper microfluidic chip for separation and simultaneous detection of three clinically relevant neurochemicals without using any decouplers.