Electrochemical UV Sensor Using Carbon Quantum Dot/Graphene Semiconductor

Abstract

Our group has developed an electrochemical UV sensor utilizing carbon quantum dots as the photoactive material functionalizing a graphene semiconductor layer. When used as a photoactive electrode in contact with a solid polymer electrolyte in a photoelectrochemical cell, illumination under UV radiation at 365 nm induces a photocurrent with a corresponding change in device voltage. The time-dependent change in voltage is a function of UV radiation intensity. Varying the UV LED power density from 26.6 mW/cm 2 (approximately 100% intensity) to 5.1 mW/cm 2 (approximately 20% intensity) results in time-dependent potential changes (dU/dt) ranging from approximately 4.0 mV/s to 0.5 mV/s. The dU/dt vs. LED power density trend is nearly linear (r 2 = 0.97). Similarly, when a constant bias potential is applied to the cell, a sustained photocurrent is observed under UV illumination, with the magnitude of the photocurrent a linear function of the LED power density. In that case, the coefficient of determination r 2 = 0.98. These results indicate that a graphene semiconductor, when functionalized with a photoactive material like carbon quantum dots, has application as a UV sensor with the ability to quantify the intensity of UV radiation. Nano-scale carbon-based materials, such as carbon quantum dots (CQDs), have received significant attention recently due to their unique optical and electronic properties.1 Depending on the particular synthesis procedure and the carbon source, carbon quantum dots can be environmentally and biologically benign.2 It is interesting to note that practically any carbon-containing material can be used as the source for carbon quantum dots. Literature reports on a host of starting materials exist. For example, Meiling and co-workers have used starch and tris-acetate-EDTA buffer as carbon sources.3 Du and co-workers prepared carbon quantum dots from orange pericarp in a hydrothermal treatment method. 4 Zhou, et al., used watermelon peel as a carbon source.5 Often, carbon quantum dots are simply obtained from more typical laboratory chemicals like citric acid. [6][7][8] There are also many possible CQD synthesis techniques, including hydrothermal methods, 9,10 electrochemical methods 11 and microwave-assisted methods.12,13 The combination of widely-variable carbon sources and facile synthesis procedures has ensured that CQD research continues to grow. It is likely that organic CQDs will make up a large share of the growing nanomaterial market. In fact, CQDs have been suggested as markers for biosensing and bioimaging, It is generally accepted that size and surface properties determine CQD optical and electronic behavior. Modification of the surface properties could be achieved by doping the CQDs, often with nitrogen. 24,25 For example, it has been demonstrated that N-doping of CQDs increases quantum yield and electron transfer.26 These N-doped CQDs (henceforth referred to as N-CQDs in this paper) possess unique properties like electrocatalytic activity, controllable luminescence and are also biologic...

Applications of Graphene Quantum Dots in Biomedical Sensors

“…Additionally, they are often used for signal amplification by serving as nanocarriers including electron transfer promoters, nanozymes, detector bioreceptors, electroactive labeling elements, and catalysts [34][35][36][37], hence offering novel strategies for biosensing platforms and their practical applicability. Over the last decade, numerous nanomaterials have been continuously studied and employed as signal-amplifying species such as nanoparticles (NPs) [38][39][40], graphene [41][42][43], nanowires [44], carbon nanotubes (CNTs) [45], magnetic beads [46,47] and quantum dots (QDs) [48,49]. Among these nanomaterials, QDs such as graphene quantum dots (GQDs) and carbon dots (CDs) are becoming quite well-known for their multifarious properties such as signal amplifying characteristics, good biocompatibility, tunable size, electro-catalytic performance as well as their capacity for the concurrent and multiple detection of biomolecules.…”

Review—Intracellular Sensors Based on Carbonaceous Nanomaterials: A Review

“…CDs or graphene quantum dots are zero-dimensional carbon nanomaterials. 63,64 Considerable attention has been paid to fluorescent CDs or graphene quantum dots owing to their small sizes (∼5 nm), low toxicity, good biocompatibility, stable photoluminescence and chemical inertness, which are advantageous over other fluorescence probes used for intracellular sensors. 20,65 In the application of intracellular sensor, CDs generally enter living cells by incubating living cells with CDs at 37 °C and then intracellular microenvironment (e.g., pH value and temperatures) or intracellular molecules or ions are analyzed by CDs through confocal fluorescence microscopic technique or electrochemistry methods.…”

Micro-photoluminescence of Carbon Dots Deposited on Twisted Double-Layer Graphene Grown by Chemical Vapor Deposition

“…However, if one wants to extend their field of application to optoelectronic devices, it is necessary to study CDs/graphene composites in the solid phase and to evaluate their interaction with target substrates. Recently, N-doped carbon quantum dots/graphene material was used as a photoactive electrode for UV sensing in an electrochemical cell . Chen et al demonstrated that adding carbon quantum dots to graphene improved the photoresponsivity of a graphene/silicon Schottky junction photodetector.…”

“…Recently, N-doped carbon quantum dots/graphene material was used as a photoactive electrode for UV sensing in an electrochemical cell. 42 Chen et al 43 demonstrated that adding carbon quantum dots to graphene improved the photoresponsivity of a graphene/silicon Schottky junction photodetector. Moreover, films composed of quantum dots of different materials (CsPbI 3 ) and micrometer-sized graphene sheets were successfully used to improve the efficiency and stability of allinorganic perovskite solar cells.…”