Photoelectrochemical Sensing Based On Functional Nano-interfaces

Photoelectrochemical analysis is a newly developed method which has the advantages ofboth photochemical and electrochemical sensors. As an analytical method, the detectionprocess of photoelectrochemistry is just the reverse of electrochemiluminescence. Light isused as excitation signal, and current is obtained as the detection signal. The backgroundsignal is reduced greatly due to the different form of energy for excitation and detection.Photoelectrochemical analysis is a very promising analytical method because of simpleequipment, low cost, easy miniaturization, high sensitivity and rapid response.Photoelectrochemical sensors are developed based on the photoelectrochemical phenomenonthat the photoelectrochemical active materials in excited states exchange electrons with theanalyte leading to the change of photocurrent. Semiconductor nanomaterials exhibit specialphotoelectrochemical properties, which are different from the bulk materials, because of thesurface effect, quantum size effect, etc. Therefore, they are widely used inphotoelectrochemical analytical system.At present, the detection principles of photoelectrochemical analysis are relativelylimited. In this paper, a new photoelectrochemial sensor based on the in-situ formation of p-njunction was designed and used for the accurate determination of mercury (Ⅱ) ions. Inaddition, the study on photoelectrochemical analysis mainly focuses on photoanode. In thispaper, we assembled two photocathodes taking advantage of different types (P or N) ofsemiconductor, and two kinds of photoelectrochemical biosensor were established based onthe change of cathodic photocurrent.The major research contents of this paper are described as follows:1. A photoelectrochemical sensor for Hg2+based on the in-situ formation of p-n junctionBecause Hg2+can increase anodic photocurrent of ZnS quantum dots, we developed asensitive photoelectrochemical sensor for Hg2+. The in-situ formation of HgS, a p-typesemiconductor, on the surface of n-type ZnS facilitated the charge carrier transfer andpromoted electron-hole separation, leading to obviously enhanced photocurrent of ZnSquantum dots modified electrode. Under the optimized experimental conditions, a good linearrelationship was obtained from0.01to10.0μmol·-1. The detection limit was4.6nmol·L-1,which was lower than the maximum permissible limit of mercy level defned for drinkingwater by WHO (around30nmol·L-1). The method was successfully applied to thedetermination of Hg2+in real samples including tap water and lake water.2. A photoelectrochemical sensor for glucose based on NiO/CdS compoundnanomaterialsIn this paper, a photocathode based on CdS quantum dots sensitized p-type NiO has beendesigned and assembled, which showed highly selective and reversible response to dissolvedoxygen in the electrolyte solution. Glucose was oxidized by dissolved oxygen under thecatalysis of glucose oxidase. The cathodic photocurrent of NiO/CdS modified electrode wassuppressed according to the decrease of dissolved oxygen which acted as electron acceptor.Based on this, we constructed a new photoelectrochemical enzyme catalytic sensor. The commonly encountered interferents such as hydrogen peroxide (H2O2), ascorbic acid (AA),cysteine (Cys), dopamine (DA) etc. almost had no effect for the cathodic photocurrent of theNiO/CdS modified electrode, which indicated greatly improved selectivity of the method. Thesensor displayed a linear response to glucose in the range from0.05to7.1mmol·L-1with adetection limit of0.01mmol·L-1. The method was applied to detect glucose in real samplesincluding serum and glucose injections with satisfactory results. This study opens a newperspective for the application of photocathode in photoelectrochemical analysis.3. A photoelectrochemical sensor for DNA based on PbS quantum dotsPt nanoparticles (NPs) and hemin which embedded into the G-quadruplex have the roleof catalase-like. They can catalyze the decomposition of H2O2, generating O2which acted asan efficient electron acceptor. Thus, the cathodic photocurrent of the PbS quantum dotsincreased, and we constructed a new photoelectrochemical sensor for target DNA based onthe phenomenon. A linear relationship between photocurrent increase and the concentration oftarget DNA was obtained in the range of1.0×10-13-1.0×10-9mol·L-1with a detection limit of4.8×10-14mol·L-1. The proposed method has good selectivity, high sensitivity and a goodapplication prospect in the construction of more other DNA sensors.