Enhancement of fast scan cyclic voltammetry detection of dopamine with tryptophan-modified electrodes

Selective and Sensitive OECT Sensors with Doped MIP-Modified GCE/MWCNT Gate Electrodes for Real-Time Detection of Serotonin

Organic electrochemical transistors (OECTs) represent a promising platform for biosensing applications in aqueous environments, including the sensitive detection of neurotransmitter molecules, such as serotonin (SE). Conventional methods for SE detection, such as HPLC and ELISA, are time-consuming and expensive. Electrochemical sensors, while sensitive and cost-effective, often struggle with real-time detection and selectivity issues due to interference from similar biomolecules, such as dopamine (DA), ascorbic acid (AA), and uric acid (UA). These interferents are particularly challenging for the OECT detection because they are easier to oxidize than SE on the gate electrode. Molecularly imprinted polymer (MIP) has gained increasing interest in electrochemical analysis, providing a cost-effective method for the selective detection of various analytes by creating matching cavities in the polymer film. Herein, a glassy carbon/multiwall carbon nanotube (GCE/MWCNT) gate electrode was modified by a PSS-doped overoxidized molecularly imprinted polymer (DOMIP) layer in an OECT sensor. Characterizations by cyclic voltammograms (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), Raman spectroscopy, and wide-angle X-ray scattering (WAXS) demonstrate an improved conductivity of the gate electrode due to DOMIP modification. The resulting GCE/MWCNT/DOMIP sensor demonstrated a low detection limit of 0.31 μM for SE in real-time measurements, comparable to that of the GCE/MWCNT sensor. However, the GCE/MWCNT sensor showed little selectivity toward SE. In addition to the SE-templated cavities, the DOMIP gate electrode modification leveraged the electrostatic interactions between the negatively charged PSS- dopant and the positively charged SE molecules to achieve a higher sensitivity toward SE compared to other negatively charged or neutral interferents in the concentration range of 0.31 μM - 3.1 μM. These findings suggest that combined with the GCE/MWCNT gate electrode, the doping strategy used in DOMIP-modified OECT sensors could provide a low-cost way for the selective and real-time monitoring of SE in complex biological samples without the usage of noble-metal electrode or expensive antibodies, which is potentially suitable for a large-scale medical diagnosis.

Identification of pyrimidine structure-based compounds as allosteric ligands of the dopamine transporter as therapeutic agents for NeuroHIV

The disruption of dopamine (DA) neurotransmission by the HIV-1 transactivator of transcription (Tat) during HIV-1 infection has been linked to the development of neurocognitive disorders, even under combined antiretroviral therapy treatment. We have demonstrated that Southern Research Institute (SRI) 32742, a novel allosteric modulator of DA transporter (DAT), attenuates cocaine- and Tat-binding to DAT, alleviates Tat-induced cognitive deficits and potentiation of cocaine reward in inducible Tat transgenic mice. The current study determined the in vitro pharmacological profile of SRI-32743 and its optimized second-generation analogs and their effects as allosteric modulators. Through structure-activity relationship studies of SRI-32743, 170 compounds were synthesized and evaluated for their ability to modulate DAT function. We identified 21 analogs as atypical competitors of DAT (maximum attributable drug effect, ≤60%). Four compounds, SRI-46564, SRI-47056, SRI-46286, and SRI-47867, displayed IC50 values for [3H]DA uptake inhibition from 9.33 ± 0.50 to 0.96 ± 0.05 μM and from 3.96 ± 1.36 to 1.29 ± 0.19 for DAT binding, respectively. The 4 analogs also displayed high potency at 2 different concentrations (0.5 nM and 0.05 nM) to attenuate Tat-induced inhibition of [3H]DA uptake and cocaine-mediated dissociation of [3H]WIN35,428 binding in Chinese hamster ovary cells expressing human DAT, suggesting that the effects occur through an allosteric mechanism. In further ex vivo studies using fast scan cyclic voltammetry, we demonstrated that the analogs do not disrupt the baseline phasic-like DA release. These findings provide a new insight into the potential for development of novel therapeutic agents to attenuate DAT-Tat interactions to normalize DA neurotransmission in NeuroHIV. SIGNIFICANCE STATEMENT: The allosteric inhibition of the dopamine (DA) transporter by the HIV-1 transactivator of transcription (Tat) disrupts DA homeostasis, leading to HIV-associated neurocognitive disorders. Analogs of Southern Research Institute 32743, a novel allosteric modulator of the Tat-DA transporter (DAT) interaction, were evaluated in the current study and characterized as atypical ligands of DA uptake. Four novel lead compounds demonstrated high potency to attenuate Tat-induced inhibition of human DAT-mediated DA uptake in an allosteric modulatory manner with no effects on the dynamics of DA uptake-release in DAT.

Developmental exposure to the Parkinson's disease-associated organochlorine pesticide dieldrin alters dopamine neurotransmission in α-synuclein pre-formed fibril (PFF)-injected mice

Parkinson's disease (PD) is the fastest-growing neurological disease worldwide, with increases outpacing aging and occurring most rapidly in recently industrialized areas, suggesting a role of environmental factors. Epidemiological, post-mortem, and mechanistic studies suggest that persistent organic pollutants, including the organochlorine pesticide dieldrin, increase PD risk. In mice, developmental dieldrin exposure causes male-specific exacerbation of neuronal susceptibility to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and synucleinopathy. Specifically, in the α-synuclein (α-syn) pre-formed fibril (PFF) model, exposure leads to increased deficits in striatal dopamine (DA) turnover and motor deficits on the challenging beam. Here, we hypothesized that alterations in DA handling contribute to the observed changes and assessed vesicular monoamine transporter 2 (VMAT2) function and DA release in this dieldrin/PFF 2-hit model. Female C57BL/6 mice were exposed to 0.3 mg/kg dieldrin or vehicle every 3 days by feeding, starting at 8 weeks of age and continuing throughout breeding, gestation, and lactation. Male offspring from independent litters underwent unilateral, intrastriatal injections of α-syn PFFs at 12 weeks of age, and vesicular 3H-DA uptake assays and fast-scan cyclic voltammetry were performed 4 months post-PFF injection. Dieldrin-induced an increase in DA release in striatal slices in PFF-injected animals, but no change in VMAT2 activity. These results suggest that developmental dieldrin exposure increases a compensatory response to synucleinopathy-triggered striatal DA loss. These findings are consistent with silent neurotoxicity, where developmental exposure to dieldrin primes the nigrostriatal striatal system to have an exacerbated response to synucleinopathy in the absence of observable changes in typical markers of nigrostriatal dysfunction and degeneration.

Ultrasensitive dopamine detection with graphene aptasensor multitransistor arrays

Detecting physiological levels of neurotransmitters in biological samples can advance our understanding of brain disorders and lead to improved diagnostics and therapeutics. However, neurotransmitter sensors for real-world applications must reliably detect low concentrations of target analytes from small volume working samples. Herein, a platform for robust and ultrasensitive detection of dopamine, an essential neurotransmitter that underlies several brain disorders, based on graphene multitransistor arrays (gMTAs) functionalized with a selective DNA aptamer is presented. High-yield scalable methodologies optimized at the wafer level were employed to integrate multiple graphene transistors on small-size chips (4.5 × 4.5 mm). The multiple sensor array configuration permits independent and simultaneous replicate measurements of the same sample that produce robust average data, reducing sources of measurement variability. This procedure allowed sensitive and reproducible dopamine detection in ultra-low concentrations from small volume samples across physiological buffers and high ionic strength complex biological samples. The obtained limit-of-detection was 1 aM (10–18) with dynamic detection ranges spanning 10 orders of magnitude up to 100 µM (10–8), and a 22 mV/decade peak sensitivity in artificial cerebral spinal fluid. Dopamine detection in dopamine-depleted brain homogenates spiked with dopamine was also possible with a LOD of 1 aM, overcoming sensitivity losses typically observed in ion-sensitive sensors in complex biological samples. Furthermore, we show that our gMTAs platform can detect minimal changes in dopamine concentrations in small working volume samples (2 µL) of cerebral spinal fluid samples obtained from a mouse model of Parkinson’s Disease. The platform presented in this work can lead the way to graphene-based neurotransmitter sensors suitable for real-world academic and pre-clinical pharmaceutical research as well as clinical diagnosis.

Vitamin C-reduced graphene oxide improves the performance and stability of multimodal neural microelectrodes

Nanocarbons are often employed as coatings for neural electrodes to enhance surface area. However, processing and integrating them into microfabrication flows requires complex and harmful chemical and heating conditions. This article presents a safe, scalable, cost-effective method to produce reduced graphene oxide (rGO) coatings using vitamin C (VC) as the reducing agent. We spray coat GO + VC mixtures onto target substrates, and then heat samples for 15 min at 150°C. The resulting rGO films have conductivities of ∼44 S cm⁻¹, and are easily integrated into an ad hoc microfabrication flow. The rGO/Au microelectrodes show ∼8x lower impedance and ∼400x higher capacitance than bare Au, resulting in significantly enhanced charge storage and injection capacity. We subsequently use rGO/Au arrays to detect dopamine in vitro, and to map cortical activity intraoperatively over rat whisker barrel cortex, demonstrating that conductive VC-rGO coatings improve the performance and stability of multimodal microelectrodes for different applications.

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Easy, scalable, and safe reduction method to create rGO films with vitamin C

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VC-rGO coatings improve the performance of bare gold microelectrodes in vitro

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VC-rGO coatings enable the voltammetric detection of dopamine on the microscale

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rGO/Au electrode arrays enable high-resolution microscale recording in vivo