Fabrication And Research Of Photoelectrochemical Biosensor Based On Semiconductor Nanomaterials

Photoelectrochemical(PEC) sensor is a newly developed analytical ptotocol, which has had a rapid development in recent years. Its sensing principle depends on the fact that the photocurrent change could be brought from the electron transfer between the illuminated PEC active materials and the analyte. The analyse process of PEC sensor is just the opposite of electrochemiluminescence. Owing to the separation of the excitation source(light) and electrochemical detection signal(photocurrent), higher sensitivity with low background signal is obtained in PEC sensor. Morever, the sensor possesses many other intrinsic advantages, such as simple and low-cost instruments, and easy miniaturization. It has received an increasing attention and possesses extensive application potential in chemical and biological analysis. Benefiting from the surface effect, quantum confinement effect, quantum size effect etc., semiconductor nanomaterials show special PEC properties which are different from the bulk materials. Consequently, more and more semiconductor nanomaterials are utilized in PEC sensors.Nowadays, the detection principles and PEC materials of the sensors are relatively limited. In this paper, a new and ultrasensitive PEC biosensor based on the signal amplification by the introduction of enzyme mimetics was fabricated firstly for the detection of antigen. Although there are many photoactive species, the research on PEC analysis mainly focuses on photoanode materials. In this paper, we explored photocathodes based on two kinds of p-type semiconductors and developed new PEC methodologies for the detection of DNA, thrombin and dopamine, respectively.The major contents of this paper are described as follows:1. An ultrasensitive and universal photoelectrochemical immunoassay based on enzyme mimetics enhanced signal amplificationThe Cd S quantum dots modified electrode was developed by the layer by layer method and then immobilized a sandwich immunocomplex via the antibody-antigen affinity interactions. The secondary antibody(Ab2, polyclonal goat antimouse Ig G) was labeled by a Pt nanoparticle(NP)-G-quadruplex/hemin probe to improved sensitivity. The probe as mimicking enzyme could catalyze the oxidation of hydroquinone(HQ) using H2O2 as an oxidant. High sensitivity for the target was achieved by a competitive nonproductive absorption of hemin and the steric hindrance caused by the polymeric oxidation products of HQ. For most important, the oxidation product of HQ acted as an efficient electron acceptor of the illuminated Cd S quantum dots. The target mouse Ig G could be detected from 0.01 pg/m L to 1.0 ng/m L with a low detection limit of 6.0 fg/m L. The as-obtained immunosensor exhibited high sensitivity and selectivity. This method has been applied to the determin the Ag in potential clinical applications such as mouse serum successfully.2. A versatile platform for photoelectrochemical aptasensing based on the photoinduced electron transfer between G-quadruplex/hemin and p-type Pb S quantum dotsWe present a novel PEC biosensing platform by taking advantage of the phenomenon that hemin intercalated in G-quadruplex could increase the cathode photocurrent of p-type Pb S quantum dots. Photoinduced electron transfer between Pb S quantum dots and G-quadruplex/hemin(III) complexes with the subsequent catalytic oxygen reduction by the reduced G-quadruplex/hemin(II) led to an obvious enhancement in the cathodic photocurrent of the Pb S QDs. For the detection process, in the presence of hemin, the specific recognition of the targets with the sensing sequence would trigger the formation of a stable G-quadruplex/hemin complex, which will result in reduced charge recombination and hence amplified photocurrent intensity of the Pb S QDs. Especially, this strategy avoided the addition of supplementary substrates of G-quadruplex/hemin such as H2O2 and organic substances, thus enhanced sensitivity of the system. The biosensor exhibited a good linear relationship to DNA in the range from 8×10-16 to 10-11 mol/L with a detection limit of 2×10-16 mol/L.Thrombin detection assays were similarly developed based on thrombin promoted binding of hemin to thrombin aptamer.3. A photoelectrochemical biosensor for highly selective detection of dopamine based on redox reaction between the dopamine and graphene oxideWe present a novel PEC biosensor based on the fact that dopamine as reducing agent could rapidly eliminate the oxygen functionality of graphene oxide to reduced graphene oxide which was functionalized by the generated polydopamine. The direct reaction of graphene oxide and dopamine allows the reduction of graphene oxide in an easy and environmentally friendly manner. The cathodic photocurrent of the graphene oxide was increased by the polydopamine as effective electron acceptor modified reduced graphene oxide. Thus, a simple PEC biosensor for dopamine detection was developed with a liner range from 0.5 to 1000 nmol/L and a detection limit of 0.23 nmol/L. Thus, the chemical reaction-based biosensor showed high selectivity for dopamine detection and was successfully applied in real human urine samples.