**3.2. Metabolite sensing from whole cells**

**2.3. Biocompatibility of CPs**

60 Green Electronics

[22, 27, 55, 58–63].

"green" and sustainable electronics future.

**3.1. Metabolite sensing of body fluids**

Among the effective presentations of organic bioelectronics, ultra-thin electronic systems for surgical, point-of-care [46], diagnostic implants [47], ambient intelligence for daily-life assistance [48], soft robotics [49], conformable and self-sustaining bioelectronic elements for sports and recreation [48], or even disposable (biodegradable) electronics [50] for food packaging [51] or throw-away applications [52] can be listed. The connection of novel electronic elements with biosensing constituents will open the possibility for investigating disposable diagnostic and drug delivery platforms. This topic has been recently reviewed in detail [53, 54]. The organic bioelectronics field may prove to be the satisfactory host for greeting natural and nature-inspired carbon materials and a perfect base for achieving the ambitious purpose of

Conducting polymers of pyrrole and thiophene connected by ester linkages have been considered for the generation of temporary scaffolds for cell attachment and proliferation for tissue engineering applications [22]. Moreover, these scaffolds are biodegradable [55]. The possibility of growing cells on CPs has proven the biocompatibility of these polymers [21, 56]. Additionally, recently the biocompatibility of PPy and PEDOT layers and PPy and PEDOT nanotubes was estimated by utilizing a dorsal root ganglion model [57]. The implantation of CPs *in vivo* for several weeks has led to only minimal inflammation, again pointing to low toxicities and good tissue compatibility [21, 55]. Moreover, Abidian and Martin [18] successfully presented that PEDOT nanotubes could record neuronal spikes about 30% more than control sites with a high signal-to-noise ratio (SNR) for 7 weeks post-implantation *in vivo*. In addition, there have been a number of reviews on CPs with regard to biomedical applications

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

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 Determination of cellular metabolites under different stimuli or environmental conditions can give useful prospects for drug discovery and toxicology. Larsen et al. used PEDOT:tosylate microelectrodes as an all polymer electrochemical chip for the determination of potassiuminduced transmitter release from neuron-like cells, presenting the potential of the procedure

**Figure 3.** Integrated point-of-care systems based on organic electronics. (A) Scheme of the conducting polymer electrochemical sensor for the direct measurement of creatinine from serum, according to [65]. (B) Schematic demonstrating the OECT-based multianalyte system, according to [67]; BSA, bovine serum albumin; ChOx, cholesterol oxidase; GOx, glucose oxidase; HRP, horseradish peroxidase; lox, lactate oxidase.

electrodes on flexible fully biodegradable silk protein fibroin supports using a simple photolithographic process and an aqueous ink composed of the CP and carrier proteins (**Figure 4B**) [78]. In an almost identical route by the same scientific group, silk proteins including fibroin and sericin were modified with photoreactive methacrylate groups for use as substrate inks for water-dispersible PEDOT:PSS that was micropatterned to investigate a biodegradable bioelectrode for glucose sensing *in vitro* [79]. This pathway presents a new trend for generating an entirely organic and free-standing system with controllable biodegradability including scalability and processability, leading to applications in wearable or implantable bioelectronics [80].

Conducting Polymers as Elements of Miniature Biocompatible Sensor

http://dx.doi.org/10.5772/intechopen.75715

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The perspectives of implantable instruments and especially home-based metabolic monitoring can only be reached if they can be simply implanted and explanted (i.e. needle-assisted) without the necessity of complicated surgery [81]. Due to that, the implantable tool should be small, which calls for novel miniaturization of different functional elements such as electrodes, power sources, signal processing systems and sensory components. In addition, miniaturized biosensors implanted by ultrafine needles induce less tissue damage and then less inflammation and foreign body response [82]. Miniaturization of implantable instruments and particularly biosensors can be listed under: (1) miniaturization of sensing electrodes and elements and (2) miniaturization of driving electronics for power, communication and their subsequent integration/packaging. Referring to the production of miniaturized electrodes for analyte sensing, immobilization of biocatalyst onto an ultra-thin Pt wire (diameters less than 50 μm) or carbon nanofibres has been substantial [83]. The latter is convenient for generating nerve stimulating microelectrodes because of the possibility of ultra-fine dimensions and flexibility [84]. Due to subsequent improvement of the electrocatalytic feature of carbon nanofibres, these were modified with different metal nanoparticles without compromising their flexibility [85]. Recently, the advent of sub-micron lithography and its further use to produce miniaturized transistors has encouraged investigators to develop solid state electrochemical sensing systems in a transistor order [86]. Biosensors based on classic Si-based transistors as well as the incipient organic thin film transistors are being investigated for a scope of analytes. The unique electrical character of 1-D nanomaterials (CPs) [86] has led researchers to use them as channel materials and investigates sensors based on modifications induced in either gate conductance, modulation, transconduction, hysteresis or threshold voltage.

The flexible nature of polymers together with their low-temperature processing and demonstrated biocompatibility with enzymes renders them beneficial over classic Si- and glass-based materials [81]. Additionally, the soft and flexible character of polymers could reduce the possibility of tissue damage to the body during implantation and can be beneficial for applications

Green electronics constitutes not only a novel term but also twenty-first century's slogan; it means an emerging area of research covered the identifying compounds of natural origin and

where the instrument has to be able to adjust itself to the shape of the human body.

**3.4. Miniaturization: implantable devices**

**4. Discussion**

**Figure 4.** Overview of the swiftly increasing field of wearable biosensors.

for drug screening applications [69]. To enhance the electrocatalytic effect of the sensing electrode, the PEDOT:PSS gate can also be supplied with electrodeposited Pt nanoparticles [70]. Owing to the high surface area of the nanoparticles and the high specificity of the biocatalyst, the authors obtained very sensitive detection of the crucial metabolites such as glucose and lactate from live cells. Lactate production in tumor cell cultures derived from real patients was also studied using an OECT circuit. Lactate production could be measured from a few cells, underlining the sensitivity of the tool in a highly complex milieu, thus shown its potential for utilization in *in vivo* applications for cancer diagnostics [71]. Also, recently, Curto et al. presented a multiparametric on-chip platform integrated with microfluidics for cell cultures, using among other in-line methods the OECT-based detection of glucose produced by the cells as a measure to validate their improved differentiation under stimuli conditions [72].
