Dual-Needle Field-Effect Transistor Biosensor for In Vivo pH Monitoring.

Local pH of the brain microenvironment is a prominent indicator for assessing health status and is closely related to many diseases; therefore, the development of effective in vivo pH methods is of great importance. This work demonstrates a dual-needle biosensor based on a solution-gate field-effect transistor (FET) for selective and sensitive monitoring of pH in cerebrospinal fluid in the central nervous system. The sensor consists of two parts: a needle FET modified with high-purity carbon nanotubes for electrical signal conduction and a needle gate modified with polyaniline for specific pH response. Based on the device's specific shape and sensing characteristics, the dual-needle sensor is sensitive to the measurement of pH in the living brain while maintaining excellent stability. The prepared dual-needle biosensor exhibits a high Nernstian response of 53.7 mV/pH over a wide pH range from 4.0 to 9.0 and excellent selectivity toward pH against other potential interfering species in the brain. Either in the case of directly injecting weak acids and bases into the rat brain or in the constructed acute acid-base poisoning model, the dual-needle biosensor can respond sensitively to the pH changes of the rat brain. This work has produced a unique dual-needle FET biosensor with high reliability and stability, which provides a new method for real-time monitoring of dynamic pH changes in the body.

Acupuncture Needle-Based Transistor Neuroprobe for In Vivo Monitoring of Neurotransmitter.

Chemical communication via neurotransmitters is central to brain functions. Nevertheless, in vivo real-time monitoring of neurotransmitters released in the brain, especially the electrochemically inactive molecules, remains a great challenge. In this work, a novel needle field-effect transistor (FET) microsensor based on an acupuncture needle is proposed, which is demonstrated to be capable of real-time monitoring dopamine molecules as well as neuropeptide Y in vivo. The FET microstructure is fabricated by successively wrapping an insulating layer and a gold layer on the top of the needle, where the needle and the Au served as the source and drain, respectively. After assembling reduced graphene oxide (RGO) between the source and drain electrodes, the specific aptamer is immobilized on the RGO, making this needle-FET biosensor highly selective and sensitive to real-time monitor neurotransmitters released from rat brain, even in a Parkinson's diseases model. Furthermore, the needle-FET biosensor is applied to detect a variety of targets including hormones, proteins, and nucleic acid. By constructing a FET sensing interface on an acupuncture needle and implanting the sensor in a rat's brain for in vivo detection, this work provides a new sight in the FET domain and further expands the species of real-time in vivo detection.

Detection of heart failure-related biomarker in whole blood with graphene field effect transistor biosensor.

Since brain natriuretic peptide (BNP) has become internationally recognized biomarkers in the diagnosis and prognosis of heart failure (HF), it is highly desirable to search for a novel sensing tool for detecting the patient's BNP level at the early stage. Here we report a platinum nanoparticles (PtNPs)-decorated reduced graphene oxide (rGO) field effect transistor (FET) biosensor coupled with a microfilter system for label-free and highly sensitive detection of BNP in whole blood. The PtNPs-decorated rGO FET sensor was obtained by drop-casting rGO onto the pre-fabricated FET chip and subsequently assembling PtNPs on the graphene surface. After anti-BNP was bound to the PtNPs surface, BNP was successfully detected by the anti-BNP immobilized FET biosensor. It was found that the developed FET biosensor was able to achieve a low detection limitation of 100fM. Moreover, BNP was successfully detected in human whole blood sample treated by a custom-made microfilter, suggesting the sensor's capability of working in a complex sample matrix. The developed FET biosensor provides a new sensing platform for protein detection, showing its potential applications in clinic sample.

Real-Time Monitoring of Nitric Oxide at Single-Cell Level with Porphyrin-Functionalized Graphene Field-Effect Transistor Biosensor.

An ultrasensitive and highly efficient assay for real-time monitoring of nitric oxide (NO) at single-cell level based on a reduced graphene oxide (RGO) and iron-porphyrin-functionalized graphene (FGPCs) field-effect transistor (FET) biosensor is reported. A layer-to-layer assembly of RGO and FGPCs on a prefabricated FET sensor surface through π-π stacking interaction allowed superior electrical conductivity caused by RGO, and highly catalytic specificity induced by metalloporphyrin, ensuring the ultrasensitive and highly specific detection of NO. The results demonstrated that the RGO/FGPCs FET biosensor was capable of real-time monitoring of NO in the range from 1 pM to 100 nM with the limit of detection as low as 1 pM in phosphate-buffered saline (PBS) and 10 pM in the cell medium, respectively. Moreover, the developed biosensor could be used for real-time monitoring of NO released from human umbilical vein endothelial cells (HUVECs) at single-cell level. Along with its miniaturized sizes, ultrasensitive characteristics, and fast response, the FET biosensor is promising as a new platform for potential biological and diagnostic applications.