Photoelectrochemical Immunosensor Based On Semiconductor - Graphene Nanocomposites

As a newly developed analytical technique, photoelectrochemical (PEC) determination strategy avoids drawbacks of expensive equipments, operation at harsh conditions, time-consuming, and difficulty for in situ or online monitoring. By using light as the external stimulus at an appropriate wavelength, a selective PEC reaction can be achieved. The complete separation of excitation source (light) and detection signal (current) can greatly reduce the undesired background signal. The PEC measurement that uses the photocurrent as a detection signal can operate at a low applied potential, and exhibit high sensitivity together with repeating cycles. Therefore, combining with PEC technique and biological recognition, the biosensor owns lots of merits, including swift response, high sensitivity, good selectivity, feasible design, miniaturization and low cost, and may show widespread application in early diagnosis of cancer. In this paper, on the basis of semiconductor-graphene nanocomposites, three PEC immunosensors with signal amplification induced by enzyme and nanomaterials were developed.1A low potential and competitive PEC biosensing platform was developed using quantum dots sensitized titanium dioxide decorated reduced graphene oxide (TiO2-RGO) nanocomposites. The nanocomposites were prepared through electrostatic interaction between mercaptoacetic acid wrapped CdSe quantum dots (QDs) with negative charge and TiO2-RGO hybrids with positive charge obtained via ultrasonic and acid treatments. Electron microscopes and spectroscopes were used to characterize the functionalized nanocomposites films of CdSe/TiO2-RGO, and the fabrication process of the PEC biosensor. Based on the high photovoltaic conversion efficiency of CdSe/Ti02-RGO nanocomposites films, after introducing biological recognition and competitive immunoreaction, a low potential and competitive PEC biosensor for carcinoembryonic antigen (CEA) detection was fabricated. The synergic effect of horseradish peroxide and benzo-4-chlorohexadienone decreased background signal, leading to signal amplification. Under the light irradiation of430nn and the applied potential of0V, it detected CEA with a linear range from0.003to100ng mL-1, and was satisfactory for clinical sample detection. The detection limit was estimated to be1.38pg mL-1at a signal-to-noise ratio of3. The proposed competitive and low potential PEC biosensor under irradiation of visible light exhibited good performance, which has promising prospect in clinical diagnose. 2On the basis of the absorption and emission spectra overlap, an enhanced resonance energy transfer caused by excition-plasmon resonance between reduced graphene oxide (RGO)-Au nanoparticles (AuNPs) and CdTe QDs was obtained. With the synergy of AuNPs and RGO as a plane-like energy acceptor, it resulted in the enhancement of energy transfer between excited CdTe QDs and RGO-AuNPs nanocomposites. After the novel sandwich-like structure was formed via DNA hybridization, the exciton produced in CdTe QDs was annihilated, and a damped photocurrent was obtained, which acted as the background signal to develop a universal PEC platform. CEA as a model which bonded to its specific aptamer and destroyed the sandwich-like structure, lowed the energy transfer efficiency, leading to PEC response augment. Thus a signal-on PEC immunosensor was constructed. Under470nm irradiation at-0.05V, the PEC immunosensor for CEA determination exhibited a linear range from0.001to2.0ng mL"1with a detection limit of0.47pg mL-1at a signal-to-noise ratio of3. The PEC immunosensor constructed by RGO-AuNPs nanocomposites and CdTe QDs showed good performance and was satisfactory for clinical sample detection. Since different aptamers can specifically bind to different target molecules, the designed strategy has an expansive application for the construction of versatile PEC platforms.3An innovative PEC platform was developed by the in situ generation of CdS QDs on GO using enzymatic reactions. Horseradish peroxidase catalyzed the oxidation of sodium thiosulfate with hydrogen peroxide for H2S generation, and then reacted with Cd2+to form CdS QDs, which could be photoexcited to generate an elevated photocurrent as readout signal. This strategy offered a "green" alternative to fussy pre-synthesis procedure for semiconductor nanoparticles fabrication. The nanomaterials and assembly procedures were adequately characterized by microscopy and spectroscopy avenues. Combining with immune recognition and based on the admirably PEC activity of CdS QDs sensitizing GO, the strategy was successfully applied to PEC assay of CEA, displaying a wide linear range from2.5ng mL-1to50μg mL-1and a detection limit of0.72ng mL-1at a signal-to-noise ratio of3. The PEC biosensor was satisfactory for clinical sample detection, and especially convenient for determination of high concentration without dilution.