Fabrication Of New Photoelectrochemical Sensing Interfaces Based On Nanomaterials

Photoelectrochemical（PEC） analysis is a newly developed and rapidly developing analytical method in recent years. As an analytical ptotocol, the detection process of photoelectrochemistry is just the reverse of electrochemiluminescence. The different form of energy for excitation and detection lead to low background signal. PEC analysis is a very promising analytical ptotocol due to its intrinsic advantages, such as simple equipment, low cost, rapid response and high sensitivity. Owing to the surface effect, quantum size effect etc., semiconductor nanomaterials exhibit special PEC properties, which are different from the bulk materials. Consequently, they are widely used in PEC sensors.Nowadays, the sensing formats and PEC materials of the PEC sensors are relatively limited. And most of photoelectrochemical detection systems rely on photoanodes of n-type semiconductors. In this paper, we explored photocathodes based on two kinds of p-type semiconductors. According to two p-type semiconductors and new PEC methodologies, we developed several new photoelectrochemical detection systems, for the detection of H₂O₂, lead（II） ion(Pb²⁺), alkaline phosphate（ALP）, tyrosinase（TR） and human α-fetoprotein（AFP）. The major contents are described as follows:1.Novel photoelectrochemical hydrogen peroxide sensor based on hemin sensitized nanoporous NiO based photocathodeA novel, facile and self–operating photocathode based on hemin sensitized three-dimensional（3D） nanoporous NiO was developed. NiO films were fabricated on conducting ITO glass substrates using the hydrothermal method and hemin molecule could bind to NiO through the conjugation of carboxyl group forming hemin sensitized NiO photocathode. Compared with pure NiO nanomaterials, the as prepared photocathode showed enhanced cathodic photocurrent under visible-light irradiation. H₂O₂（electron acceptor） can accept an electron from excited state of hemin which will result in enhanced cathodic photocurrent. Thus, a simple, sensitive and selective PEC biosensor for detecting H₂O₂ was developed. The ITO/NiO/hemin electrode showed a linear range of 0.5–500.0 μmol/L with a low detection limit of 0.1 μmol/L for the detection of H₂O₂. In addition, the method was also successfully applied to the detection of H₂O₂ in real samples（milk and eye drop） with satisfactory results.2. A photoelectrochemical sensor for lead（II） ion based on the in situ generation of photosensitizerPb²⁺ induces the allosteric transition of K+-stabilized G-quadruplex intercalated with hemin, which releases hemin to sensitize the p-type NiO electrode, forming the self-operating photocathode which will result in enhanced cathodic photocurrent. The release of more hemin leads to bigger cathodic photocurrent. Thus, a sensitive and selective PEC biosensor for detecting Pb²⁺ was developed. The cathodic photocurrent linearly increases with the concentration of Pb²⁺ in the range of 20.0 to 1500.0 nmol/L with a detection limit of 4.0 nmol/L. This study not only opens up the application of self-operating photocathode in metal ion sensing, but also it introduces a new concept of constructing PEC strategy based on in situ generation of photosensitizer.3. A photoelectrochemical sensor for high sensitive detection of ALP, TR and AFP based on redox reactionCatechol（CA） could reduce graphene oxide（GO） to generate poly（catechol） functionalized reduced graphene oxide（RGO） which will result in enhanced cathodic photocurrent. Besides that, ALP molecules could hydrolyze the o-phosphonoxyphenol（OPP） to CA, using this hydrolysis, a highly sensitive sensor was developed for detection of ALP. The detection limit of ALP was 0.0013 U/L. In addition, this detecting method was expanded to AFP immunoassay. The hybridization chain reaction（HCR） and the enzyme reaction constituted the signal amplification for a very highly sensitive AFP detection. The detection limit of AFP was 0.15 fg/mL（S/N=3）. The detection of TR were similarly developed based on the facts that levodopa could reduce graphene oxide to generate functionalized RGO leading to the cathodic photocurrent of GO modified electrode greatly enhanced and tyrosinase catalyzes the oxidation of tyrosine to levodopa. The detection limit of TR was 0.09 U/L. The PEC sensors exhibited good sensitivity and selectivity. In addition, it manifested advantages of without labelling/immobilization of recognition elements on the electrodes.