Study On Electrochemical/Photoelectrochemical Biosensor For Detection Of Heavy Metal Ions

Electrochemical（EC）biosensing platforms have attracted extensive interest of researchers in recent years du e to their advantages of fast response,convenient operation,low cost,and high sensitivity.With the rapid development of materials and bio-nanotechnology,the development of photoelectric materials provides opportunities for the application of biosensor s.Among them,photoelectrochemical（PEC）biosensors are a new type of electrochemical biosensors developed from electrochemical sensors that combine optoelectronic materials and electrochemical technologies.When sensor is working,the optoelectronic materials are excited by light to generate photocurrent,and the modified antibody,nucleic acid or aptamer on the electrode acts as a recognition unit and reacts with the target to generate corresponding electrical signal changes to realize detection of the t arget.Since the energy types of excitation source and signal source are different and their devices are completely separated,the PEC sensor has the advantages of low background signal and high sensitivity.In recent years,the detection of heavy metal io ns has become one of the most concerned public health issues due to the threat to human health caused by heavy metal ions in the environment.Water quality safety has far-reaching significance for the long-term development of human beings,other organisms and the ecological environment.As people become more and more aware of the importance of water environment quality,the development of simple,sensitive and accurate detection technology is of great importance for the detection of heavy metal ions.In this paper,two different sensing strategy platforms are designed to realize the sensitive analysis of Pb²⁺and Hg²⁺.（1）A titanium-based metal-organic framework（MOF）material（NH₂-MIL-125）with large surface area and porosity was used as a template.Cu²⁺was introduced into the NH₂-MIL-125 through chelation with the amino group of NH ₂-MIL-125.Then Cu₂O-Cu O-Ti O₂ heterojunctions were synthesized by calcining Cu²⁺/NH₂-MIL-125.Based on the good optoelectronic properties of the Cu ₂O-Cu O-Ti O₂ heterojunction,a label-free ultra-low background noise of PEC biosensing platform for Pb²⁺determination was developed.When the target Pb²⁺exists,the Pb²⁺substrate chain（Pb-Sub）can be cleaved,and a small amount of the target can be converted into a large number of output DNA single strands（S1）by means of Pb²⁺-assisted circular amplification strategy and magnetic separation.Efficient conversion between target and output signals is achieved.S1 can hybridize with HP1 on the electrode,so that the hairpin chain of HP1 is opened,and the exposed phosphate group on the HP1 chain adsorbs Cu₂O-Cu O-Ti O₂,thus a large cathodic photocurrent is observed,which promotes the sensitive detection of Pb²⁺.The photocurrent response is linear with the concentration of Pb²⁺from 10 f M to 1μM with a detection limit of 6.8 f M.In addition,this PEC biosensor exhibits high selectivity,stability,good reproducibility,and analytical applicability.The developed PEC biosensing platform has application potential in environmental water sample analysis.（2）A dual-mode biosensing platform combining EC and PEC sensing mechanisms was developed to achieve sensitive and reliable detection of Hg²⁺.A/R-Ti O₂ heterojunctions derived from NH₂-MIL-125 were used as substrate materials,and methylene blue（MB）labeled on single-stranded DNA was used as a bifunctional probe.In the presence of Hg²⁺,the MB-labeled T-rich single-stranded DNA hybridizes with the T-rich single-stranded DNA on aminated Ti O₂,resulting in the MB being close to the electrode surface,leading to an electrochemical response signal and an enhancement of the photocurrent.The as-prepared EC-PEC dual-mode biosensor showed a wide linear response range and low detection limit（a linear response range of 0.5 n M to 10μM and a detection limit of 30 p M for EC method;a linear response range of 0.01 n M to 10μM with a detection limit of 2.4 p M for PEC method）.The EC-PEC dual-mode biosensing platform based on the MB bifunctional probe has good selectivity,reproducibility and stability,a nd has potential application value for the detection of environmental water samples.