Space charge capacitance and the physical mechanism of negative capacitance in organic light-emitting diodes (OLEDs) by transient current response analysis are investigated for the first time.

The high electron mobility transistor (HEMT)-based biosensors are highly competitive in the ultimate application of portable and point-of-care testing. Herein, we have demonstrated highly sensitive and real-time detection of cardiac troponin I (cTnI), a biomarker for the diagnosis of acute myocardial infarction (AMI) using AlGaAs/GaAs HEMT-based biosensors. The device has achieved a lower detection limit of 1 pg/ml in the buffer solution and less than 30 s response time, which demonstrated significant promise in the early diagnosis and screening of AMI. In addition, our results are consistent with the enzyme-linked immunosorbent assay according to the AMI patient’s blood test results. Furthermore, by comparing the two HEMT structures, we also calculated the equilibrium dissociation constant (K_D) of the cTnI and cTnI antibody and analyzed the sensing mechanism. The results show that this method is very promising for early diagnosis of AMI.

Herein, we designed several structures of GaAs/AlGaAs extended gate high electron mobility transistors (EG-HEMT) for cTnI detection, in order to explore the mechanism of bio-detection, the limit of detection (LOD) as well as the application in clinical detection. The experiment carried out that 50y structure of EG-HEMT biosensor, whose extended electrode is 50 times as large as the gate, has highest biological regulation ability ( δ). Meanwhile, the concentration range of cTnI detection using 50y EG-HEMT biosensor is about 100 fg ml ^-1 to 10 μg ml ^-1 , which is much broader than that of Unicel Dxl800 (usually be used in clinical detection). Furthermore, due to the influence of parasitic resistance and other factors, δ increases with the increase of y, but the rising rate of δ decreases at the same time. By comparing the detecting results of clinical samples, 30y EG-HEMT is the best in the detection of cTnI concentration with a relative error of 6%. In a higher concentration range, it is more accurate than that of the Unicel Dxl800, breaking through its limit.