Coaxial fiber organic electrochemical transistor with high transconductance

Fiber organic electrochemical transistors(OECTs)have received extensive attention in wearable and implantable biosensors because of their high flexibility and low working voltage.However,the transconductance of fiber OECTs is much lower compared with the planar counterparts,leading to low sensitivity.Here,we developed fiber OECTs in a coaxial configuration with microscale channel length to achieve the highest transconductance of 135 mS,which is one to two orders of magnitude higher than that of the state-of-the-art fiber OECTs.Coaxial fiber OECT based sensors showed high sensitivities of 12.78,20.53 and 3.78 mA/decade to ascorbic acid,hydrogen peroxide and glucose,respectively.These fiber OECTs were woven into a fabric to monitor the glucose in sweat during exercise and implanted in mouse brain to detect ascorbic acid.This coaxial architectural design offers an effective way to promote the performance of fiber OECTs and realize highly sensitive detection of biochemicals.

Fiber-shaped organic electrochemical transistors for biochemical detections with high sensitivity and stability

Precise and continuous monitoring of biochemicals by biosensors assists to understand physiological functions for various diagnostics and therapeutic applications.For implanted biosensors,small size and flexibility are essential for minimizing tissue damage and achieving accurate detection.However,the active surface area of sensor decreases as the sensor becomes smaller,which will increase the impedance and decrease the signal to noise ratio,resulting in a poor detection limit.Taking advantages of local amplification effect,organic electrochemical transistors(OECTs)constitute promising candidates for high-sensitive monitoring.However,their detections in deep tissues are rarely reported.Herein,we report a family of implantable,fiber-shaped all-in-one OECTs based on carbon nanotube fibers for versatile biochemical detection including H2O2,glucose,dopamine and glutamate.These fiber-shaped OECTs demonstrated high sensitivity,dynamical stability in physiological environment and antiinterference capability.After implantation in mouse brain,7-day dopamine monitoring in vivo was realized for the first time.These fiber-shaped OECTs could be great additions to the"life science"tool box and represent promising avenue for biomedical monitoring.

Long-term In Vivo Monitoring of Chemicals with Fiber Sensors

Long-term in vivo monitoring of chemicals with implanted sensors has received considerable interests over the past decades owing to their significant contributions in reflecting health conditions and assistance in diagnosing diseases.However,the widely explored chemical sensors outside the body fail to meet the requirements of in vivo applications.This perspective reviews main challenges,recent advances and future directions of long-term in vivo monitoring of chemicals,related to immune response and sensing performance.Challenges in terms of the immune response caused by unstable interfaces between sensors and tissues and improper implanting methods,and the insufficient performance of chemical sensors in complex physiological environment are discussed.Therewith,recent advances in fabricating biocompatible,flexible and thin sensors,developing effective implanting methods with reduced injury and improving the sensitivity,selectivity and stability of chemical sensors for accurate monitoring in vivo are summarized.Finally,we propose the future directions to address these challenges by fiber chemical sensors through the combination of soft fiber configuration,facile implanting methods and new recognition elements,which will provide new platforms for health monitoring and physiological mechanism revealing.

Responsive Polymer Composite Fiber

Wearable devices are a mainstream for our future daily life,where responsive polymer composite fibers represent one of the key components.However,their practical applications are hampered by several challenges,including poor responsive reversibility,poor controllability and low stability as well as single function.Herein,we share our recent studies on overcoming the above challenges for achieving novel responsive polymer composite fibers,especially focusing on chromatic fibers,deformational fibers and their integrations.Furthermore,we introduce a type of novel materials for these responsive fiber materials,i.e.,aligned carbon nanotube sheets and fibers simultaneously with excellent electrical,optical and mechanical properties.For the future development,we further highlight the possible directions in this field.

Implantable Fiber Biosensors Based on Carbon Nanotubes

CONSPECTUS:Implantable biosensors represent a rapidly developing direction with a wide range of applications in biotechnology and life science.For example,the detection of neurotransmitters in the brain has attracted a lot of attention because of their essential effects for neural activity.The in vivo acute detection of chemicals has been developed for decades,but there are few reports about in vivo chronic monitoring of chemicals probably due to two reasons.First,it is difficult to form stable interfaces between biosensors and tissues.Specifically,most of implantable biosensors are based on stiff electrode materials such as carbon fibers,whose moduli are several orders of magnitude higher than these of soft biological tissues.The mechanical mismatch between them will cause severe inflammatory response during chronic applications.Although some flexible neural probes with mesh geometry consisting of polymer and metal and polymer composite fibers have been employed in chronic electrophysiological recording,they are rarely employed for chronic monitoring of chemicals.Second,electrode deteriorations associated with degradation and fouling of functional materials make chemical recognitions difficult in dynamic environment.Generally,biosensors usually need to be modified with several functional materials including a recognition layer in order to identify specific chemicals from various untargeted chemicals.Although nanomaterials with high surface areas are reported to enhance the loading and immobilization of recognition layers so as to improve the sensitivity of biosensors,nanostructured and soft microelectrodes with high specific surface areas are rarely employed for longterm monitoring of chemicals in vivo.In this Account,we highlight our efforts toward flexible and miniaturized implantable fiber biosensors based on carbon nanotube(CNT)fibers for stable interfaces in vivo.We first summarize the assembly structure of CNT fiber electrodes and their mechanical,electrical,electrochemical,and biocompatible properties.Then we present a family of fiber biosensors by modifying CNT fibers with different recognition materials to detect multiple chemicals in vivo.After that,all-in-one fiber organic electrochemical transistors are described with higher sensitivity and lower detection limit,aiming to detect chemicals with low concentrations and trace changes in the deep brain.Finally,considering that soft implantable biosensors are difficult to be implanted without assistance,we introduce a neural probe with alterable moduli for direct implantation into the mouse brain and forming a stable interface with brain tissues.All three kinds of fiber biosensors are soft with mechanical properties matching biological tissues,remaining stable under deformation and showing high biocompatibility for long-term in vivo applications.Finally,a brief summary of challenges and outlooks in this field is presented.

Flexible dopamine-sensing fiber based on potentiometric method for long-term detection in vivo

Achieving real-time,continuous and long-term monitoring of dopamine(DA)in vivo is essential for revealing brain functions and preventing and treating neurogenic diseases.However,it remains challenging to achieve a low limit of detection(LOD)and high neuron-compatibility at the same time for the current microsensors,resulting in the failure of long-term and accurate detection of DA in vivo.A DA-sensing fiber was achieved by the potentiometric method to possess a low LOD of 5 nM,1-3 orders of magnitude lower than amperometry and differential-pulse voltammetry.The sensing fiber showed a wide linear range from 5 to 185 nM that well matched the DA concentration(26-40 nM)in vivo.After implantation,the sensing fiber showed no influence on the firing rates of neurons with the potentiometric test,indicating high neuron-compatibility.It was then integrated with electrophysiology to simultaneously monitor DA variation and electrical signal in the brain,with stable monitoring of DA change in vivo for 8 weeks.The sensing fiber was flexible and stably worked after hundreds of bending,and it showed high sensitivity even after protein adsorption,thus offering a reliable tool for neuroscience.