Study On Novel Optical Biosensors For Heavy Metal Mercury, Bisphenol A Detection

The harm of heavy metal pollution to ecological environment and human health has caused widespread attention. Mercury is strongest toxicity in heavy metal ion, which can cause harm to human body even in low concentration. Besides, Bisphenol A（BPA） have estrogen-like properties, and can invade into the food or beverage easily, so BPA pollution may result in the damage of central nervous system and reproductive immune system of person or animal. Therefore, the development of detection methods for BPA and Hg²⁺ can be necessary and significant. In order to Sensitively detect the target, novel strategy based on aptamer, with high specificity, good stability, flexible convert mechanism, has been extensive researched by scholars. In this paper, combined with the specificity, stronger binding force of aptamer, and the physico-chemical property of nanometer materials and polymer, different ways for detection of Hg²⁺ and BPA were explored with variety of ways of energy conversion, which are listed as following. 1. Colorimetric detection of Hg²⁺ based on PDDA and AuNPsA novel strategy is proposed based on the aggregation of gold nanoparticles（AuNPs） driven by a cationic polymer. DNA combines electrostatically with phthalic diglycol diacrylate（PDDA） in a solution of AuNPs. In the presence of Hg²⁺, thymine（T）-Hg²⁺-T induced hairpin turns are formed in the DNA strands, which then do not interact with PDDA, enabling the freed PDDA to subsequently facilitate aggregation of the AuNPs. Thus, according to the change in color from wine-red to blue-purple upon AuNPs aggregation, a colorimetric sensor is established to detect Hg²⁺. Under optimal conditions, a linear range of 0.25-500 nM was obtained by absorption spectroscopy with a detection limit of approximately 0.15 nM. Additionally, the proposed method shows high selectivity toward Hg²⁺ in the presence of other heavy metal ions. Real sample analysis was evaluated and the results suggest good potential for practical application. 2. Colorimetric detection of Hg²⁺ based on Eexonuclease Ⅲ and T-Hg²⁺-TIn this part, we constructed a biosensor for detection of Hg²⁺, which is based on circular amplification of signal cased by the shearing action of Eexonuclease Ⅲ（ExoⅢ） to dsDNA that formed by T-Hg²⁺-T, and the catalysis of G-quadruplex to ABTS and H2O2. With increase of Hg²⁺ concentration, the shear effect of ExoⅢ to dsDNA is enhanced, this will result in the amount of G-quadruplex increased, which make the absorption of system changed more apparent. Therefore, the developed method have good linear detection range of 0.05-1 ng/mL according to interaction between absorption value and Hg²⁺ concentration. The actual samples tested recovery was 98.3 106.2%. Besides, the Hg²⁺ can be detected by the method with good specificity. 3. fluorescence detection of BPA based on GO and anti-BPA aptamer.A kind of new method for detection of BPA was designed based on graphene oxide and anti-BPA aptamer. The graphene oxide can specifically adsorb and quench the fluorescence of fluorescently modified ssDNA probes. Meanwhile, the BPA can combine with anti-BPA optamer and switch its configuration to prevent the aptamer from adsorbing on the surface of graphene oxide（GO）. Under different concentrations of BPA, based on the target-induced conformational change of anti-BPA aptamer and the interactions between the fluorescently modified anti-BPA aptamer（FAM-ssDNA） and GO, the experimental results show that the intensity of the fluorescence signal was changed. A low limit of detection of 0.05 ng/mL was obtained in the range 0.1-10 ng/mL. In addition, the specificity was outstanding among analogues of BPA. The recovery rate in actual water samples spiked with BPA can be 96.0% to 104.5%. The developed method was successfully used to determine BPA in actual water samples...