**3. Organic electronic-based sensing platforms for body metabolites**

#### **3.1. Metabolite sensing of body fluids**

Blood is the most generally used body fluid for metabolite level monitoring. Nevertheless, owing to the wealth of electroactive elements, electrochemical determination procedures become somewhat challenging, and the usually observed biofouling of the sensing electrodes poses further restrictions [5, 64]. CPs bearing sustainable surface modifications (i.e. incorporation of electron mediators, permselective membranes) can offer precious instruments towards modern and more accurate diagnostic devices. An antibody-mediated amperometric platform was designed by Wei et al. to avoid the interfering signals often encountered in complex systems (blood) when utilizing enzymatic-mediated amperometric determination. A PPy matrix favored for immobilization of the capture antibody, on top of a 16-array gold electrochemical sensor, which could therefore determine creatinine fast and accurately in whole blood, resulting in a point-of-care (POC) assay for allograft dysfunction (**Figure 3A**) [65]. Liao et al. recently investigated a flexible organic electrochemical transistor **(**OECT) platform based on PEDOT:PSS to selective detection of urea and glucose in saliva samples [66]. To exclude electrochemical interference in saliva, thus increasing sensitivity and selectivity, the gate electrodes were modified with oppositely charged bilayer polymeric layers for both anionic and cationic charge exclusion of interferes. Moving towards multiplexing, a PEDOT:PSS-based OECT biosensing platform integrated with microfluidics was investigated for contemporary screening of glucose, lactate and cholesterol in human saliva samples [5]. The final tool was tested with human volunteers before and after exercise to present comparative differences in their metabolite profiles under stimuli (**Figure 3B**) [67]. In a similar procedure, contemporary sensing of lactate and glucose was presented by integrating two OECT-based tools, each with a separate microfluidic channel. They created a prototype portable glucose sensor by linking a smartphone with the sensing platform through Bluetooth connection, highlighting the ease of integration of such devices for POC systems [68].
