Flexible Wearable Photo/Electrochemical Biosensor Based On Porphyrin MOFs For Sweat Detection

Vitamin C and glucose are both essential nutrients that people require to maintain the health of themselves.Vitamin C helps the growth of bones and blood vessels,and is remarkable for treating scurvy,anemia,and swollen joints;glucose is good for metabolism and strengthening memory,and is often used by medical practitioners as a quick energy supplement.Because of their importance to the human body,how to achieve real-time detection of these nutrients becomes a great concern.Although traditional blood tests are more reliable,they have the disadvantage of invasiveness,which brings discomfort and the risk of cross-contamination.In addition,bulky and expensive specialized equipment is not conducive to testing efficiency.Therefore,the development of completely non-invasive,simple and quick on-site testing methods is needed,and hopes are pinned on the development of wearable sweat sensors to change the status quo.Metal organic frameworks(MOFs)are porous materials formed by coordination of metal nodes with organic ligands.The structural properties of porosity and high specific surface area make MOFs have great potential for applications in biochemical sensing.In particular,porphyrin-based MOFs generally have good photoelectric conversion ability,which lays the foundation for photoelectrochemical(PEC)sensing via MOFs.Porphyrin MOFs showed wide applicability and promising market prospects for PEC sensing and EC sensing applications.In this paper,we used ZnTCPP(Zn)MOF and ZnTCPP(Fe)MOF as substrates to achieve the detection of vitamin C and glucose concentrations by PEC and EC sensing strategies.The main studies are as follows:(1)An enzyme-free wearable photoelectrochemical sensor based on zinc porphyrin MOF nanosheets driven by smartphone light is proposed for continuous sweat vitamin C detection.The two-dimensional porphyrin MOF(2D-TCPP(Zn))with zinc as the node can stably generate electron-hole pairs upon stimulation by a light source.The remarkable photoelectric conversion ability was used to promote the oxidation reaction of vitamin C in sweat.With the introduction of multi-walled carbon nanotubes(MCNTs),the electron transfer efficiency in2D-TCPP(Zn)was greatly improved,and the developed 2D-TCPP(Zn)/MCNTs exhibited a satisfactory enhanced cathodic photocurrent response to vitamin C under smartphone light irradiation.Substrate material plays an important role in the design of wearable sensors,paper and fabric are considered as ideal substrates with the advantages of low cost,flexibility and hydrophilicity.Therefore,we fabricated a highly integrated paper electrode sensing patch.Due to the strong water absorption and storage capacity of filter paper and non-woven fabrics,sweat can be transported and diffused along the axial direction,reducing the discomfort caused by the accumulation of sweat on the skin surface.In this work,the smartphone is both the initiator of the excitation signal and the receiver of the response signal.To the best of our knowledge,this is the first attempt to combine a smartphone-based wearable enzyme-free sensor with the PEC strategy.The experimental results show that our sensor can accurately measure the change of vitamin C concentration in sweat,which is expected to be applied in personalized daily health management.(2)A bimetallic MOF with zinc porphyrin as the ligand and iron ions as the node(ZnTCPP(Fe))was synthesized by a solvothermal method,and the MXene/PDA/ZnTCPP(Fe)composite was obtained by tightly binding the MOF to MXene nanosheets through the adsorption of polydopamine(PDA).Combined with flexible indium tin oxide(ITO)electrode and sweat-absorbing hydrogel,a vitamin C and glucose sensor based on PEC and EC sensing strategies was constructed.MXene/PDA/ZnTCPP(Fe)exhibited stable cathodic photocurrent response to vitamin C when irradiated by a cell phone light source,and the cascade reaction of MXene/PDA/ZnTCPP(Fe)with glucose oxidase enabled it to exhibit excellent reduction current response to glucose without light source irradiation.MXene significantly enhances the response strength due to its high conductivity,the PDA protects MXene from oxidation in the air environment while providing excellent adsorption,extending the composite lifetime.Transparent ITO film electrodes ensure that light transmission is not reduced,and the flexible combination with sweat-absorbing hydrogel allows perfect fit to the body for wearable sensing.Currently,multiple bio-sample testing has attracted much attention.Experimental results show that the PEC/EC sensor can effectively monitor vitamin C and glucose in sweat,and has the potential for application in guiding people to make wise dietary choices.