Isabel Álvarez-Martos

Electrochemical Label-Free Aptasensor for Specific Analysis of Dopamine in Serum in the Presence of Structurally Related Neurotransmitters

Cellular and brain metabolism of dopamine can be correlated with a number of neurodegenerative disorders, and as such, in vivo analysis of dopamine in the presence of structurally related neurotransmitters (NT) represents a holy grail of neuroscience. Interference from those NTs generally does not allow selective electroanalysis of dopamine, which redox transformation overlaps with those of other catecholamines. In our previous work, we reported an electrochemical RNA-aptamer-based biosensor for specific analysis of dopamine (Analytical Chemistry, 2013; Vol. 85, p 121). However, the overall design of the biosensor restricted its stability and impeded its operation in serum. Here, we show that specific biorecognition and electroanalysis of dopamine in serum can be performed by the RNA aptamer tethered to cysteamine-modified gold electrodes via the alkanethiol linker. The stabilized dopamine aptasensor allowed continuous 20 h amperometric analysis of dopamine in 10% serum within the physiologically important 0.1-1 μM range and in the presence of catechol and such dopamine precursors and metabolites as norepinephrine and l-DOPA. In a flow-injection mode, the aptasensor response to dopamine was ∼1 s, the sensitivity of analysis, optimized by adjusting the aptamer surface coverage, was 67 ± 1 nA μM(-1) cm(-2), and the dopamine LOD was 62 nM. The proposed design of the aptasensor, exploiting both the aptamer alkanethiol tethering to the electrode and screening of the catecholamine-aptamer electrostatic interactions, allows direct monitoring of dopamine levels in biological fluids in the presence of competitive NT and thus may be further applicable in biomedical research.

Seawater operating bio-photovoltaic cells coupling semiconductor photoanodes and enzymatic biocathodes

Access to fresh water and energy is ranked as one of the most severe challenges to humankind. The restricted availability of fossil fuels and clean water does not match the increasing energy demands and growing population needs, which, desirably, should be satisfied in the most sustainable, clean and inexpensive way. Here, we report clean and sustainable conversion of solar energy into electricity by photo- and bio-electrocatalytic recycling of the H2O/O2 redox couple in a hybrid bio-photovoltaic (BPV) membraneless cell comprising a sunlight-illuminated water-oxidizing semiconductor anode (either Zn-doped hematite or TiO2) and an oxygen-reducing enzymatic biocathode, in such environmental media as seawater. Upon simulated solar light illumination (AM 1.5G, 100 mW cm−2), the maximum power density (Pmax) generated by the cell was 236 and 21.4 μW cm−2 in 1 M Tris–HCl and seawater, both at pH 8, respectively. In seawater its ionic content inhibited mostly the activity of the photoanode, but not that of the biocathode. The obtained Pmax values were orders of magnitude higher than those of a photo-electrochemical cell with a Pt mesh cathode (0.32 μW cm−2 in seawater). The demonstrated thermodynamically feasible coupling of cost-effective photoactive materials such as TiO2 or hematite semiconductors and enzymatic counterparts in seawater media opens a prospective clean and sustainable way of transformation of the most abundant, clean and renewable source of energy – solar light – and the Earths most massive water resource – seawater – into electricity, which can also be used for fresh water production.