| The pH of the brain microenvironment is closely related to various life activities and functions of the brain.Acid-base disorders of the brain microenvironment affect many important physiological activities such as signal transduction,cell growth and apoptosis,enzyme activity and ion transport in brain regions.Such disturbances are also commonly associated with the development of brain disorders such as epilepsy,ischemia and mental disorders,significantly increasing patient morbidity and mortality through many protonsensitive processes such as ion channel gating,synaptic transmission,and intercellular communication.Real-time monitoring of pH changes in the living brain is clinically important to help explore the pathological processes of acidbase disorders and facilitate in situ and direct in vivo signals for disease progression and treatment.However,in vivo monitoring device is the bottleneck to explore the association between acid-base fluctuations in the brain and pathophysiology.Therefore,there is an urgent need to develop novel detection devices for real-time monitoring of pH changes in the living brain to provide informative information for disease progression.The primary requirement for in vivo pH detection devices is that the devices are small enough to be placed in vivo for real-time dynamic monitoring.Secondly,living organisms contain a variety of interfering substances such as proteins and ions,which requires in vivo detection devices that can sensitively detect hydrogen ions in a complex environment.Based on the above requirements for in vivo detection devices,this study utilizes the advantages of high sensitivity,good specificity,low cost,label-free and easy miniaturization of field-effect transistor(FET)biosensor,and uses traditional acupuncture needles as the sensing substrate for design and optimization to develop a dualneedle type field-effect transistor biosensor for monitoring real-time pH changes in the central nervous system of rat brain.The sensor consists of two parts: a needle field-effect transistor modified with carbon nanotube(CNT)for electrical signal sensing and transmission,and a needle platinum(Pt)gate modified with polyaniline(PAN)for further increasing the sensor response to hydrogen ions.This dual-needle field-effect transistor not only provides highly sensitive pH monitoring in vivo,but also minimizes damage to the organism.The specific research of this topic is divided into two parts as follows:Part ?: Preparation and basic property characterization of double-needle field effect transistor biosensor.Medical acupuncture needles were selected as the substrate of the sensor,and the surface of the needles was coated several times using vacuum vapor deposition and electroplating techniques to form a stainless steel-Parylene-AuParylene four-layer structure.Using sandpaper and a micro-electrode beveling machine to grind a smooth cross-section of the processed needle tip,the ground cross-section of the needle-type FET can be observed from the inside to the outside as stainless steel,Parylene layer,Au layer,and Parylene layer,where the stainless-steel layer and Au layer are used as the drain and source of the FET,and the Parylene layer sandwiched between them is used as the sensing channel.Subsequently,carbon nanotubes of semiconducting nature are deposited on the sensing interface of the needle-type FET to complete the preparation of the needle-type CNT-FET.To further improve the sensitivity and specificity of the device to hydrogen ions,we continue to modify polyaniline on the gate to complete the PAN/Pt gate fabrication.The combination of the needle CNT-FET and the PAN/Pt gate constitutes a dual-needle field-effect transistor capable of highly sensitive sensing of pH.In this study,the successful construction of the needle CNT-FET and the needle PAN/Pt gate was demonstrated using characterization methods such as scanning electron microscopy.Electrical tests characterized the dual-needle field-effect transistor from another perspective,and the device exhibited the unique transfer characteristic curve and output characteristic curve of carbon nanotubes under bias and gate pressure,demonstrating the field-effect performance of the sensor.To further verify the pH sensing capability of the sensor,we examined the buffer pH using the dual-needle field effect transistor.The results show that the Nernst response of the dual-needle field effect transistor is 53.7 m V/pH,while the Nernst response of the conventional needle CNT-FET is only 27.3 m V/pH.The response of the dual-needle field effect transistor to hydrogen ions is the superposition of the solution interface and the polyaniline membrane interface response,and the synergistic effect of the two makes the dual-needle field effect transistor have more excellent sensing performance.Real-time detection of the pH buffer using the sensor has also yielded stable and sensitive results.The reversibility and reusability of the sensor were also verified through a series of experiments.The results of the first part of the experiments demonstrate the good performance of the constructed dual-needle field effect transistor for pH detection and lay the foundation for the subsequent in vivo experiments.Part ?: Real-time monitoring of acid-base disturbance in rat brain by a dual-needle field effect transistor biosensor.The purpose of this part is to apply the biosensor prepared above to live rat brain for real-time pH detection.To this end,we further explored the specificity,anti-interference,and in vivo stability of the sensor for hydrogen ion detection.The results showed that the device responds specifically to hydrogen ions even in the presence of other ions or neurotransmitters,which demonstrates that the sensor has good selectivity for hydrogen ions.The sensor was able to produce a good signal response to pH in simulated serum,with a Nengst response of48.5 m V/pH,proving that the device has excellent interference immunity.The ability of the sensor to maintain a sensitive response to pH even after a long period of in vivo measurement indicates that the device has good stability.Based on the above-mentioned excellent properties of the sensor,we utilized it for real-time detection of acid-base disorders in the rat brain.First,we placed the sensor and the injection needle in the striatum of the rat brain,and used the syringe to directly pump weak acid and weak base into the rat brain to cause direct pH changes in the rat brain,and the sensor could make sensitive current changes in the rat brain in response to the acid-base changes,and the detection results were statistically different.We then placed the sensor in the cerebral cortex and constructed acute acidosis and acute alkalosis models using direct inhalation of carbon dioxide and intraperitoneal injection of sodium bicarbonate,respectively.When the sensor was used to detect the acute acidbase disorder in the model rats,the device was also able to generate the corresponding current signal and the results were statistically different.The above in vivo experiments demonstrated that the dual-needle field effect transistor was successful in detecting acid-base disorders in rat brain in realtime with its excellent sensitivity,specificity,stability,interference resistance and device miniaturization.In this paper,a dual-needle field effect transistor biosensor was successfully prepared based on acupuncture needles,and it can be applied to monitor the dynamic level changes of intracerebral pH in real time in vivo,which provides a new idea for in vivo real-time detection. |
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