Construction And Performance Analysis Of Biosensors Based On AuNPs/MnO₂ Nanosheets

Biosensor can be used to detect various biomolecules.The biggest advantage of biosensor is that it integrates biology,chemistry,physics and other related technologies.With the application of nanomaterials,the biosensing technology has been greatly developed.When the size of the material is reduced to nanoscale,it exhibits unique physicochemical properties due to the surface roughness and specific surface area.Up till now,various nanomaterials have been widely used in the construction of biosensors,including AuNPs,MnO2 nanosheets,metal organic frame nanomaterials,precious metal nanomaterials and nanoclusters.In this paper,we have developed a series of simple,economical and highly sensitive biosensors based on the excellent physical and chemical properties of AuNPs and MnO2 nanosheets.Details are as follows:1.The localized surface plasmon resonance(LSPR)effect of AuNPs is closely related to its morphology and size,which has been widely used in the construction of colorimetric biosensors.Two kinds of colorimetric biosensors for drugs detection were developed.We first designed a strategy based on PDDA-AuNPs to achieve a highly sensitive detection of heparin.Furthermore,a more specific colorimetric strategy for theophylline detection was proposed.This strategy demonstrated excellent detection performance,such as rapid response time,outstanding selectivity,as well as extremely low limit of detection(LOD).In addition,these strategies exhibited favourable practicability in human serum samples.2.Since the aberrant expression of miRNA is closely related to the occurrence and development of tumor,miRNA can serve as a common tumor biomarker.The monitoring of miRNA expression levels is crucial for early diagnosis and therapy of cancer.Therefore,we constructed two independent colorimetric biosensors based on cross-linking(CA)and non-cross-linking aggregation(NCA)of AuNPs for multiplex miRNA detection.Firstly,a multi-miRNA colorimetric system based on CA aggregation of AuNPs was developed.Furthermore,NCA of AuNPs was used as a signal indicator element for miRNA detection.The proposed method abandoned the tedious DNA modification process,and utilized hybridization chain reaction(HCR)to improve the sensitivity.3.As an important gene regulatory element,mRNA is a reliable biomarker of disease.However,the analysis of mRNA in living cells is not easy to achieve due to its purification or cellular fixation.Therefore,we proposed a strategy for mRNA quantification and intracellular imaging based on 1D-HCR.Afterwards,we developed a simpler and faster fluorescence method based on 2D-HCR.In addition,we designed a single-stranded region on each DNA probe to ensure that this region could be effectively adsorbed onto the MnO2 nanosheets.These multifunctional mRNA detection strategies can not only serve as practical tools for real-time monitoring of intracellular mRNA,but also provide novel ideas for the development of other nucleic acid analysis methods.4.DNA adsorption on the surface of MnO2 nanosheets is of great significance for biosensing,bioimaging and disease treatment.Here,biological interface interactions between salt concentration,pH,temperature,DNA concentration and length on DNA@MnO2 nanosheets were systematically studied using UV-vis absorption spectra.Subsequently,optimal parameters were used to construct a novel electrochemical PCR system for ultrasensitive detection of circulating tumor DNA(ctDNA).In this method,MnO2 nanosheets were used to modify the screen-printed electrode(SPE).Advantages of SPE,DNA@MnO2 nanosheets and PCR amplification reaction were integrated,with LOD as low as 0.1 fM.This strategy exhibited broad application prospects in biological analysis,clinical disease diagnosis,biomedicine and other fields.5.AuNPs and MnO2 nanosheets are commonly used as color indicators in colorimetric biosensors.Herein,the relationship between DNA and AuNPs salt tolerance was systematically investigated through UV-vis absorption spectrum.According to the results,we developed a novel DNAzyme@HCR colorimetric sensing system based on LSPR of AuNPs for miRNA detection,with LOD of 0.1 nM.In addition,we developed another colorimetric sensing platform for miRNA detection based on the superstability of DNA-AuNPs and the high extinction coefficient of MnO2 nanosheets.Results of the detection can be observed by the naked eye,thereby making it have great application potential.Furthermore,this method can pave the new way for the application of composite nanomaterials.