## 2 Organic Electrochemical Transistors (OECTs)
In another recent work, thanks to monolithic integration of a Au working/sensing electrode, an on-chip Ag/AgCl reference electrode, and Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) counter electrode--which also functions as the channel of an organic electrochemical transistor--[PERSON] and colleagues have developed a device that simultaneously performs OECT testing along with traditional electroanalytical techniques such as cyclic voltammetry and square-wave voltammetry. This device allows for the direct amplification of current from an electrochemical aptamer-based sensor through in-plane current modulation within the counter electrode/transistor channel. The integrated sensor can detect transforming growth factor beta 1 with a sensitivity improvement of 3 to 4 orders of magnitude compared to traditional electrochemical aptamer-based sensors (292 \(\mu\)A/dec versus 85 nA/dec). This versatile approach is applicable to a broad range of tethered electrochemical reporter-based sensors, enhancing their sensitivity, enabling miniaturization, and simplifying the signal processing [33]. [PERSON] et al. introduce a paper-based ion-selective organic electrochemical transistor (IS-OECT) that has been highly optimized to achieve outstanding analytical performance. By integrating thick-film transistor technology with precise adjustments to the ion-selective membrane's composition and thickness, the device achieves sensitivities of up to 2.50 mA/decade. This level of sensitivity exceeds that of other similar devices reported so far by over an order of magnitude. The system demonstrates excellent selectivity, allowing for the detection of low potassium concentrations even in highly saline environments, with a linear detection range from 0.1 mM to 100 mM. This range effectively encompasses the clinically relevant concentrations of K+ in blood. Additionally, a calibration curve for K+ in artificial serum from 1 to 10 mM shows the device's ability to detect concentration changes as small as 0.05 mM. The fabrication process for this IS-OECT is simple, utilizing techniques such as drop casting on inexpensive substrate materials, and the device operates efficiently with a gate voltage of 0 V. These features position the IS-OECT as a promising candidate for ion-sensing applications in point-of-care settings [34]. Apart from that, there are a lot of more important examples about the use of novel OECTs in biosensing applications, corroborating the enormous potential in this field and the booming interest in the scientific community [35; 36; 37; 38]. In recent years, apart from bioelectronics, there has been a rise in the use of lightweight, wearable, and low-power OLEDs in on-skin medical applications, such as cancer treatment and muscle-contraction sensors for robotics. All-organic flexible devices offer an alternative to traditional rigid oximetry sensors. In today's world, there is a growing demand for excellent in situ and noninvasive sensors, a market where OECTs present intriguing prospects. Since these devices need to be in contact with the skin or other biological systems, it is essential to ensure specific material properties. Additionally, device architectures must be compatible with the mechanical stress they will face. Long-term durability is also a key consideration. In the quest for wearable and portable devices, one of the key challenges is printing these devices directly onto fabrics. An early breakthrough in this area was made by [PERSON] and colleagues, who developed a non-invasive OECT sensor integrated into textiles through a one-step screen-printing process. Their work successfully detected various biomarkers, including adrenaline, dopamine, and ascorbic acid, in both biological fluids and synthetic sweat, demonstrating similar sensitivity to conventional flat OECTs. Moreover, these sensors operated at low voltage and showed remarkable stability even after repeated hand-washing, highlighting their potential as wearable biosensors [39].