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.This work was funded by: "la Caixa" Banking Foundation under grant agree ment LCF/PR/HR21-00410; national funds, through the Foundation for Science and Technology (FCT)—projects UIDB/50026/2020, UIDP/50026/2020, and UIDB/04650/2020; by FCT project PTDC/MED-NEU/28073/2017 (POCI-01-307 0145-FEDER-028073); by The Branco Weiss fellowship—Society in Science (ETH Zurich); and by FCT Ph.D. fellowships SFRH/BD/14536/2022 (M.A.), SFRH/BD/08181/2020 (T.D.), and PD/BD/127823/2016 (D.R.)

One-dimensional TiO2 nanostructured photoanode for dye-sensitized solar cells by hydrothermal synthesis

One-dimensional nanostructured photoanode in the dye-sensitized solar cell (DSSC) provides better electron transport and lifetime. One-dimension TiO2 nanostructures (1D-TNs) were prepared by single-step hydrothermal synthesis for 10 h using titanium(IV) isopropoxide (TTIP) and titanium(IV) chloride (TiCl4) as the precursor. Nano parallelepiped TiO2 film was uniformly grown on the substrate which was ball milled to increase the specific surface area to felicitate sufficient dye-loading for efficient DSSC. The synthesized nanostructures were characterized by scanning and transmission electron microscopy and X-ray diffraction. Photovoltaic properties of DSSC with prepared TiO2 1D-TNs as the active layer, N719 dye and Pt counter electrode was investigated. The power conversion efficiency of the prepared cells was measured by using solar simulator under standard test conditions (100 mW/cm(2), AM 1.5). The cell performance can be maximized by optimizing the thickness of 1D-TNs photoanode. The promising power conversion efficiency of 5.77% was obtained with the photoanode of 5 mu m thickness

Cu2ZnSnSe4 QDs sensitized electrospun porous TiO2 nanofibers as photoanode for high performance QDSC

An earth-abundant and relatively less toxic, quatemary Cu2ZnSnSe4 (CZTSe) quantum dots (QDs) were prepared by hot injection method at low temperature to use as a sensitizer for QDSC. The formation of tetragonal phase and stoichiometry were confirmed by X-ray diffraction (XRD), Raman spectroscopy and energy dispersive X-ray (EDX) analysis, respectively. The UV-Vis-NIR and photoluminescence spectroscopy was used to determine the bandgap (1.66 eV) and narrow emission (1050-1130 nm) range. Moreover, transmission electron microscopy (TEM) was used to find out the average size of CZTSe QDs and it was found to be similar to( )5 nm. It can highly adsorb on the porous TiO2 nanofibers (NFs) and enhance the absorbance due to its smaller size. The photoconversion efficiency was investigated using the prepared CZTSe QDs sensitized porous TiO2 NFs based QDSC and its photoconversion efficiency (PCE) was found to be 3.61% which is higher than that of the conventional TiO2 NFs based QDSC (eta approximate to 2.84%)

Synthesis and characterization of carbon based counter electrode for dye sensitized solar cells (DSSCs) using sugar free as a carbon material

Dye sensitized solar cells (DSSCs) are a low cost alternative to silicon-based and thin film solar cells. Usually DSSCs utilize platinum to catalyze the iodine redox couple and complete the electric circuit. Though, platinum is an excellent catalytic material for use in preparation of counter electrodes (CEs) for DSSCs but it is expensive. Alternatives to replacement of platinum (Pt) that have been examined are carbon materials, conductive polymers. In this work, counter electrode for DSSCs was fabricated using carbon material obtained from carbonization of sugar free at high temperature. Slurry of the carbon produced by carbonization was made with polyvinylpyrrolidone (PVP) as a surfactant and a coating was obtained by doctor blading the slurry over the FTO glass substrate. The DSSCs based on produced carbon CE show a maximum power conversion efficiency of 6.72% (area 0.25 cm(2)), which is comparable to 8.19% of the cell with the conventional Pt CE at the same experimental conditions. The current density (Jsc) and open circuit voltage (V-oc) of the DSSCs was 17.10 mA cm(-2) and 0.66 V respectively. (C) 2017 Elsevier Ltd. All rights reserved

Influence of PVP template on the formation of porous TiO2 nanofibers by electrospinning technique for dye-sensitized solar cell

The porous TiO2 nanofibers were prepared by electrospinning technique using polyvinylpyrrolidone (PVP) as template as well as pore-forming agent at the calcination temperature of 475 A degrees C for 5 h. The influence of various concentrations of PVP (5, 8 and 10 wt%) on the surface area and porosity of the prepared TiO2 nanofibers (NFs) were studied by using BET-specific surface area analyzer. The TiO2 NFs obtained by using 5 wt% of PVP had higher surface area and porosity than those obtained by using 8 and 10 wt% of PVP. The prepared electrospun TiO2 NFs were characterized by using TG analysis, X-ray diffraction, FTIR, FE-SEM and TEM studies. Finally, dye-sensitized solar cells were assembled using the prepared TiO2 NFs as the photoanode, Pt as the cathode and 0.5 M 1-butyl-3-methylimidazolium iodide, 0.5 M LiI, 0.05 M I-2, 0.5 M 4-tertbutylpyridine in acetonitrile as an electrolyte. Among the three photoanodes, the cell assembled using porous TiO2 NFs obtained by using 5 wt% of PVP showed higher power conversion efficiency (PCE) of 4.81 % than those obtained by using 8 and 10 wt% of PVP, which showed the lower PCE of 4.13 and 3.42 %, respectively

High efficiency dye sensitized solar cell made by carbon derived from sucrose

Carbon materials represent an attractive alternative to platinum based counter electrodes in DSSCs. Graphitic carbon produced from carbonization of sucrose has been used for making counter electrode for DSSCs. It was observed that increment in thickness of carbon counter electrode improves the performance of DSSCs. Electrochemical impedance spectroscopy, Tafel polarization and cyclic voltammetry measurements suggest that sucrose derived carbon based counter electrode shows fast reduction rate of I-(3) over bar compare with platinum based counter electrode. DSSCs based on sucrose derived carbon exhibit high power conversion efficiency (PCE) of 9.96% and fill factor (FF) of 0.72 which is higher than PCE of 9.39% and FF of 0.67 of the cells with platinum (Pt) based counter electrode. (C) 2017 Elsevier B.V. All rights reserved

Few layers graphene based conductive composite inks for Pt free stainless steel counter electrodes for DSSC

FTO and platinum free steel counter electrode substrate based dye-sensitized solar cells (DSSC) are fabricated with few layers graphene (FLG) composite conductive inks. FLG are synthesized by liquid phase high shear exfoliation and the FLG based composite conducting inks are formulated with multi walled carbon nanotubes (MWCNT) and carbon black (CB) in polyimide matrix. The developed ink formulations are suitable for high temperature processing at 500 degrees C which enables to form graphene based composite conducting films on steel. Polyamic acid (PAA) intermediate layer provides superior adherence and potentio-dynamic polarization studies suggest that PAA coating also provides barrier layer and passivates the corrosion rate. Dye sensitized solar cells have been fabricated with these graphene composite coated on steel substrates which serves as the back electrodes. The cyclic voltammetry (CV) results of FLG composite conductive ink coated steel shows encouraging catalytic activity for the redox reaction of I-/I-3(-) redox mediator. The developed FLG based composite ink formulations and fabrication of working DSSCs with conducting graphene composite coated steel substrate can be a potential step towards the realization of Pt free large area roof top DSSCs

Liquid phase high shear exfoliated graphene nanoplatelets as counter electrode material for dye-sensitized solar cells

Graphene nanoplatelets (GNPs) are prepared from natural graphite by a simple and low-cost liquid phase high shear exfoliation method. The as-prepared GNPs are used as a counter electrode (CE) material for dye-sensitized solar cells (DSSCs). To confirm the Exfoliated GNPs, structural and morphological studies are carried out using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) studies. The electrochemical behaviour of GNPs as a counter electrode material is evaluated and compared with standard Platinum (Pt) electrode using cyclic-voltammetry (CV) and electrochemical impedance spectroscopy (EIS). These studies indicated that electrocatalytic activity towards redox mediator exhibited by the GNPs based electrode is comparable to standard Pt counter electrodes. DSSCs are fabricated using the counter electrodes made of GNPs and the photo-conversion efficiency is found to be 6.23% under standard test conditions, which is comparable to Pt based DSSCs proving them as potential alternative materials for counter electrodes. (C) 2017 Published by Elsevier Inc