# Diamonds for Life: Developments in Sensors for Biomolecules
## 6 Discussion and Future Outlook  
The electrical detection of biomolecules using diamond-based devices can be done either with simple electrodes or with target-specific biosensors, as reviewed in the present work. Electrodes built from BDD (Section 4) can serve as practical, resilient, and reusable instruments in bioanalytical applications because of their unique electrochemical properties, chemical stability, and 'anti-fouling' behaviour. Unlike the biosensors described in Section 5, these electrodes are not functionalised for target-specific analysis, their optimisation being attained by finding the oxidation (or reduction) peak voltage of the desired analyte and operating under that voltage. This raises the obvious question of selectivity, particularly for the electrodes described in Sections 4.1-4.4, which were only evaluated _in chimico_, that is, in buffered solutions containing either just the target analyte or mixtures of the analyte with one or two common interferents. Their ability to operate in complex biological matrices, such as biological fluids or even in a living tissue, remains to be demonstrated, being an important target of investigation for those aiming to pursue further studies in this field. A second important issue is their sensitivity (LOD and/or linearity range), because biologic amines exist in very low quantities in the human body. Plasma levels of dopamine range between 0.05 and 0.3 nM [58], while plasma noradrenaline is within 0.9 to 8 nM [59]. These values are below, or within close proximity of, the linear response range of the electrodes, thus meaning that their applicability to real-case scenarios with plasma samples will require a pretreatment step to increase the concentration of the analyte, or the improvement of their performance. The approach employed by [PERSON] et al. is a possible strategy for curbing these issues: by coating the electrode surface with an anionic polymer, the LOD was successfully lowered to the femtomolar range; however, the linear response range was still quite high, within the micromolar range [36], warranting further improvement. A recent strategy to overcome reduced sensitivity was recently presented by [PERSON] et al. [60]. Using an oil-membrane composite protection chamber, interferences from the biofluid of hydrophilic solutes and solvents were mitigated. This oil-membrane protection allowed lowering the LOD of two standard inorganic compounds, hexacyanoferrate (II/III) and hexaammineruthenium (II/III), by over 100-fold compared to traditional electrodes (that is, those that were not covered with the membrane/oil chamber) [60]. While this concept was only demonstrated for the two inorganic standards, it is an innovative and promising approach for detecting biomolecules in biofluids with fewer performance-diminishing interferent effects; moreover, it does not require the change of the biosensor system itself, relying, instead, on the use of a careful selection of the semi-permeable membrane and oil composition for each specific application. Electrodes described in Sections 4.5-4.7 constitute interesting proofs-of-concept on the application of diamond-based devices for sensing biological transmitters. The adenosine electrode, tested by [PERSON] et al. on excised rat brain tissue and shown to operate within the nanomolar range [51], may also find use in monitoring plasma adenosine levels, typically around 0.6-1.1 mM [61]. The NADH sensor (Section 4.6) also operates in the nanomolar range. Further emphasis should be given to the electrode reposted by [PERSON] et al. (Section 4.7), already demonstrated to operate in vivo with promising results in cancer detection [52]. In the case of diamond-based biosensors, specificity of response is implemented by design, because the response relies on a specific interaction between the analyte and a complementary biomolecule on the organic receptor layer.