Construction Of Bipolar Electrochemiluminescence Sensors And Its Application In Physiological Index Detection

Electrochemiluminescence has been extensively employed in biochip,immunoassay,drug and biochemical analysis due to its fast response,high sensitivity and good controllability.However,most electrochemiluminescence sensors are based on traditional three-electrode systems.The same region of the working electrode combines the dual functions of capturing targets and interface electric-optical energy conversion.It inevitably affects the accuracy of the test results.At the same time,the high sensitivity of electrochemiluminescence sensing technology inevitably amplifies the interference signal.In recent years,closed bipolar electrodes have been proposed and used in construction of electrochemiluminescence sensors.The separated cathode and anode regions of c-BPE were set as the detection pole and the signal pole,which effectively shielded the mutual interference between different reactions.Therefore,sensitive and accurate detection of actual samples based on electrochemiluminescence technology has been realized.At present,bipolar electrochemiluminescence sensors have been utilized for determination of small molecules,nucleic acids,proteins and cells.In this paper,the bipolar electrodes were selected as the research object and a series of bipolar electrochemiluminescence sensors were built.We focused on improvement of sensing performance from the aspects of electrode materials,sensor composition,and device design.Furthermore,the established sensing platforms were used in different application scenarios to verify their practicability.In this paper,three different types of sensors were constructed,namely a ratiometric sensor,a dual-mode sensor and a multi-functional sensor.In virtue of the separated anode and cathode reaction chambers,the interference between the two electrochemiluminescence systems was avoided in the ratio sensor.The mutual interference between different detection means was avoided in the dual-mode sensor.And the interference between the sample environment and reagents was avoided in the multi-functional sensor.Among them,the dual-signal ratio sensor realized high stability and accurate detection.The dual-mode sensor achieved dual-mode signal output of electrochemiluminescence and colorimetry.In the multi-functional sensor,a flexible bipolar electrochemiluminescence sweat component detection unit was constructed by using hydrogel.Combined with the stretchability,adhesion and strain sensing characteristics of hydrogel itself,the application of hydrogel in monitoring of motion behavior was extended,realizing the comprehensive evaluation of motion behavior and sweat composition.First,a ratiometric bipolar electrochemiluminescence sensor was developed by constructing a set of electrochemiluminescence detection system at both ends of the bipolar electrode.Molecularly imprinted polymer was modified at the anode of the bipolar electrode to specifically recognize ascorbic acid,while Ru（bpy）₃²⁺in the anolyte was used to provide the electrochemiluminescence signal of the anode.Zn In₂S₄was modified at the cathode surface for providing the electrochemiluminescence signal of the cathode.Re-exposure of anode to ascorbic acid led to decrease of the anode signal,while the cathode signal increased,forming the ratio sensing mode.Under the optimal conditions,the prepared bipolar electrochemical sensor showed a good linear relationship for ascorbic acid samples from 50 n M to 3 m M.It has been verified that the relative standard deviation of the detection results obtained by the ratio sensing method was 15 times and 5 times lower in repeatability and long-term stability than that obtained by the single-pole detection method.In addition,the sensor achieved highly sensitive and accurate detection of ascorbic acid in actual bovine serum samples by combining the ratiometric construction concept and molecular imprinting technology.Zn In₂S₄was used as an electrochemiluminescence reagent to construct electrochemiluminescence sensors for the first time.It is worth noting that without any additional sensitization modification,the detection limit of the sensor can meet actual sample detection requirements,avoiding the errors caused by excessive electrode surface modification on the detection results.Secondly,a dual-mode sensor was constructed by setting an electrochemiluminescence detection system and a colorimetric detection system at both ends of the bipolar electrode.Luminol in the bipolar electrode anolyte provided the electrochemiluminescence signal,while the Prussian blue modified on the cathode surface provided the colorimetric signal.The sensor had two detection modes:“dual-mode”detection mode for one analyte and“dual-target”detection mode for two analytes.Two common physiological analytes（glucose and lactic acid）were used as model analytes to investigate the“dual-mode”sensing performance of the sensor.Compared with the single detection method,the“dual-mode”detection method had a wider response range,and the output results of the two detection methods can be mutually verified.Two important physiological indicators of typeⅣhyperlipidemia（very low density lipoprotein and acetylcholinesterase）were used as model analytes to investigate the“dual target”sensing performance of the sensor.The two detection modes of the sensor were proved to be feasible,and the contents of glucose in bovine serum and NADH and hydrogen peroxide in He La cells were detected.Finally,a hydrogel-based flexible bipolar electrochemiluminescence sensor was fabricated by improving the prepared materials of bipolar electrodes.Considering the potential of hydrogels in motion behavior monitoring,a multi-functional sensor consisting of a physical detection unit and a biochemical detection unit was established.In this work,two different doped hydrogels were synthesized,namely the hydrogel doped with redox graphene and the hydrogel doped with the luminescent reagent-luminol.The former constituted a strain sensing unit for measuring movement behavior and completed sweat collection during the process.Subsequently,the two differently doped hydrogels spontaneously healed to form a hydrogel-based bipolar electrode and further constituted a sweat sensing unit.In practical application,the motion monitoring unit possessed good detection continuity and can effectively capture real-time motion behavior.The sweat detection unit realized the accurate detection of urea,lactic acid and chloride ions in sweat.In addition,the hydrogel-based electrochemiluminescence system displayed significant advantages in stability and luminescence duration compared with rigid electrode-based systems.Under the same excitation conditions,the signal intensity of the tenth response collected from the rigid electrode system was only 74.6%of the original signal,while that from the hydrogel system was 92.6%of its original signal.At the same time,the response duration of the hydrogel system was more than twice as long as that of the rigid electrode system.