COMPETITIVE ENZYME-LINKED IMMUNOSORBENT ASSAY FOR A SELECTIVE AND SENSITIVE DETERMINATION OF DOPAMINE IN THE PRESENCE OF ASCORBIC ACID AND URIC ACID

A disposable sensor based on one-pot synthesized tungsten oxide nanostructure-modified screen printed electrodes for selective detection of dopamine and uric acid

Here, screen-printed carbon electrodes (SPCEs) were modified with ultrafine and mainly mono-disperse sea urchin-like tungsten oxide (SUWO3) nanostructures synthesized by a simple one-pot hydrothermal method for non-enzymatic detection of dopamine (DA) and uric acid (UA) in synthetic urine. Sea urchin-like nanostructures were clearly observed in scanning electron microscope images and WO3 composition was confirmed with XRD, Raman, FTIR and UV-Vis spectrophotometer. Modification of SPCEs with SUWO3 nanostructures via the drop-casting method clearly reduced the Rct value of the electrodes, lowered the ∆Ep and enhanced the DA oxidation current due to high electrocatalytic activity. As a result, SUWO3/SPCEs enabled highly sensitive non-enzymatic detection of DA (LOD: 51.4 nM and sensitivity: 127 µA mM-1 cm-2) and UA (LOD: 253 nM and sensitivity: 55.9 µA mM-1 cm-2) at low concentration. Lastly, SUWO3/SPCEs were tested with synthetic urine, in which acceptable recoveries for both molecules (94.02-105.8%) were obtained. Given the high selectivity, the sensor has the potential to be used for highly sensitive simultaneous detection of DA and UA in real biological samples.

A novel protective modality against rotenone-induced Parkinson's disease: A pre-clinical study with dulaglutide

Parkinson's disease (PD) drugs treat symptoms without inhibiting progression. In recent years, finding novel therapeutic medications that can halt disease progression has become crucial. Research on antidiabetic medicines is valuable in these investigations because of the parallels between the two disorders. Using Rotenone (ROT), a frequently used PD model, the possible neuroprotective benefits of Dulaglutide (DUL), an extended-acting glucagon-like peptide-1 agonist, were considered. Twenty-four rats were randomly assigned to 4 groups to complete this experiment (n = 6). 0.2 ml of the vehicle (1 ml of dimethyl sulfoxide (DMSO) diluted in sunflower oil) was administered to the standard control group subcutaneously with a 48-hour pause. The second group was administered ROT 2.5 mg/kg SC every 48 h for 20 days as a positive control group. The third and fourth groups were administered one dose of DUL each week (0.05 and 0.1 mg/kg SC, respectively) to their regimens. The mice received ROT (2.5 mg/kg SC) every 48 h for 20 days after receiving DUL for the initial dose (96 h later). The current study focused on the DUL's ability to preserve usual behavioral function, enhance antioxidant and anti-inflammatory pathways, inhibit alpha-synuclein (α-syn), and increase parkin levels. It is concluded that DUL acts as an antioxidant and an anti-inflammatory to protect against ROT-induced PD. However, more studies are required to support this finding.

Plier Ligands for Trapping Neurotransmitters into Complexes for Sensitive Analysis by SERS Spectroscopy

Catecholamines-dopamine, noradrenaline and adrenaline are important biomarkers of neurotransmitter metabolism, indicating neuroendocrine tumors and neurodegenerative diseases. Surface-enhanced Raman spectroscopy (SERS) is a promising analytical technique with unprecedented multiplexing capabilities. However, not all important analytes exhibit strong SERS signals on stable and robust nanostructured substrates. In this work, we propose a novel indicator system based on the formation of mixed ligand complexes with bispidine-based bis-azole ligands which can serve as pliers to trap Cu(II) ions and stabilize its complexes with catecholamines. Four synthesized ligands with different functional groups: carboxyl, amino, benzyl, and methoxybenzyl, were applied for forming stable complexes to shift maximum absorbance of catecholamines from the ultraviolet region to 570-600 nm. A new absorbance band in the visible range resonates with the local surface plasmon resonance (LSPR) band of metal nanoparticles and most used laser wavelengths. This match allowed use of Molecular Immobilization and Resonant Raman Amplification by Complex-Loaded Enhancers (MIRRACLE) methodology to measure intense Raman signals on a nanostructured silver-based SERS-active substrate. The synthesized plier-like ligands fixed and stabilized catecholamine complexes with Cu(II) on the SERS sensor surface, which facilitated the determination of dopamine in a 3.2 × 10^-12-1 × 10^-8 M concentration range.

Breaking the barrier to biomolecule limit-of-detection via 3D printed multi-length-scale graphene-coated electrodes

Sensing of clinically relevant biomolecules such as neurotransmitters at low concentrations can enable an early detection and treatment of a range of diseases. Several nanostructures are being explored by researchers to detect biomolecules at sensitivities beyond the picomolar range. It is recognized, however, that nanostructuring of surfaces alone is not sufficient to enhance sensor sensitivities down to the femtomolar level. In this paper, we break this barrier/limit by introducing a sensing platform that uses a multi-length-scale electrode architecture consisting of 3D printed silver micropillars decorated with graphene nanoflakes and use it to demonstrate the detection of dopamine at a limit-of-detection of 500 attomoles. The graphene provides a high surface area at nanoscale, while micropillar array accelerates the interaction of diffusing analyte molecules with the electrode at low concentrations. The hierarchical electrode architecture introduced in this work opens the possibility of detecting biomolecules at ultralow concentrations.

Colorimetric monitoring of serum dopamine with promotion activity of gold nanocluster-based nanozymes

Over the past few decades, metal nanoparticles have been actively investigated as enzyme mimetic nanomaterials. However, the catalytic activity of gold nanocluster (AuNCs)-based nanozymes is relatively low. It is still a great challenge to improve the enzyme-mimic catalytic property of AuNCs, and to explore the roles of the charges on the surface of the nanozymes and reactive oxygen species in the catalytic reaction systems. This study describes a simple synthesis of AuNCs capped with papain (P@AuNCs). The as-prepared P@AuNCs exhibited an efficient peroxidase-mimic ability via the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide. Interestingly, the negatively charged dopamine was able to trigger the aggregration of the positively charged P@AuNCs and reactive oxygen species generated in the oxidation process, resulting in a remarkable catalytic activity promotion of P@AuNCs. Based on this principle, a protocol for the highly selective and sensitive monitoring of dopamine has been constructed with the colour change from pale blue to deep blue. The ultraviolet-visible absorbance of P@AuNCs-TMB at the wavelength of 650 nm showed a good linear relationship with the dopamine concentration ranging from 2.0 μM to 25.0 μM (R² = 0.990). The limit of detection was 0.8 μM. Furthermore, dopamine was monitored in a drug metabolic process following the abdominal injection in rats using the proposed colorimetric assay. It offers an easy approach for the fabrication of AuNCs-based nanozymes with an improved catalytic activity, and provides a great potential application in the measuring of real serum drugs.

Competitive method for fluorescent dopamine detection in cerebrospinal fluid based on the peroxidase-like activity of ficin

Dopamine (DA), a catecholamine neurotransmitter, is considered to be an important indicator for mental diseases detection in the clinic. In this study, a novel fluorescent sensing platform consisting of the ficin-H₂O₂-tyramine system for determining DA in cerebrospinal fluids (CSF) was established. The proposed method is based on the fact that ficin, a mimetic peroxidase, can catalyze H₂O₂ decomposition into OH radicals, which can oxidize non-fluorescent tyramine into fluorescent dityramine. When DA was introduced, DA can compete with tyramine for OH and resulting in the oxidation reaction of tyramine inhibited along with the fluorescence intensity of the system decreased, which provides a unique strategy for fluorescence detection of DA. Under optimal conditions, the fluorescence intensity decreased linearly with the DA level over a wide concentration range from 0.05 to 12.0 μM (R² = 0.995) with a detection limit of 46 nM (3σ/k). More importantly, the proposed sensing approach exhibits high sensitivity, good selectivity and has been successfully applied to DA sensing in complex biological samples, which made it hold great potential for DA determination in chemical and biological analytical applications.

Regioselective plasmonic nano-assemblies for bimodal sub-femtomolar dopamine detection

Reliable and ultrasensitive quantification of dopamine (DA) is essential in the precise diagnotherapy of neurological diseases. In this study, dual mode counterpropagating-responsive gold@silver nanoparticle-gold nanorod (Au@AgNP-AuNR) nano-assemblies were fabricated for the precise quantification of DA. The plasmonic Au@AgNP-AuNR assemblies possessed high surface-enhanced Raman scattering (SERS) activity and strong fluorescence quenching, due to the prominent electromagnetic enhancement between the hotspots of the assemblies. In the presence of a DA target, the Au@AgNP-AuNR assemblies dissociated, leading to an increase in fluorescence intensity and a decrease in SERS intensity. The limit of detection (LOD) of DA was 0.04 fM and 0.02 fM by the fluorescence method and SERS method, respectively. The linear range was 0.1-10 fM. These findings demonstrated that the simultaneous positive fluorescence response and negative SERS response ensured the accurate detection of DA, which opens up a new avenue for the early diagnotherapy of neurological diseases.

A novel optical biosensor for direct and selective determination of serotonin in serum by Solid Surface-Room Temperature Phosphorescence

This paper describes a novel biosensor which combines the use of nanotechnology (non-woven nanofibre mat) with Solid Surface-Room Temperature Phosphorescence (SS-RTP) measurement for the determination of serotonin in human serum. The developed biosensor is simple and can be directly applied in serum; only requires a simple clean-up protocol. Therefore it is the first time that serotonin is analysed directly in serum with a non-enzymatic technique. This new approach is based on the covalent immobilization of serotonin directly from serum on a functional nanofibre material (Tiss®-Link) with a preactivated surface for direct covalent immobilization of primary and secondary amines, and the subsequent measurement of serotonin phosphorescent emission from the solid surface. The phosphorescent detection allows avoiding the interference from any fluorescence emission or scattering light from any molecule present in the serum sample which can be also immobilised on the nanofibre material. The determination of serotonin with this SS-RTP sensor overcomes some limitations, such as large interference from the matrix and high cost and complexity of many of the methods widely used for serotonin analysis. The potential applicability of the sensor in the clinical diagnosis was demonstrated by analysing serum samples from seven healthy volunteers. The method was validated with an external reference laboratory, obtaining a correlation coefficient of 0.997 which indicates excellent correlation between the two methods.