Cholesterol as a Promising Alternative Energy Source: Bioelectrocatalytic Oxidation Using NAD-Dependent Cholesterol Dehydrogenase in Human Serum

Abstract

Cholesterol is an essential structural component of mammalian cells, although elevated concentrations of cholesterol in the human body are linked to atherosclerotic disease. In this context, monitoring physiological cholesterol concentrations is of great interest in medical fields and the concept of producing electrical energy from cholesterol is interesting. In this work, we report the bioelectrocatalytic oxidation of cholesterol with the use of nicotinamide adenine dinucleotide-(NAD) dependent cholesterol dehydrogenase (ChDH) as an alternative enzyme to the commonly-used cholesterol oxidase (ChOx) in bioelectronic applications. To achieve bioelectrocatalytic cholesterol oxidation, ChDH was combined with diaphorase (DH) in a bilayer fashion, whereby DH acts as an intermediary enzyme to facilitate NADH oxidation at a ferrocene redox polymer. Characterization of the resulting bioanode identifies a linear cholesterol response range from 5 μM to 200 μM, with an associated sensitivity of 60.12 mA cm −2 M −1 . Furthermore, an O 2 -reducing biocathode incorporating bilirubin oxidase (BOx) was combined with the cholesterol bioanode into a complete cholesterol/O 2 membrane-less enzymatic fuel cell (EFC).

Efficient NADH Regeneration by a Redox Polymer-Immobilized Enzymatic System

“…Redox polymers, in contrast, have shown promise and have been used in both NAD + and NADH cofactor regeneration. Diaphorase has been immobilized by redox polymers containing osmium − and ferrocene , to mediate electrons in the oxidation of NADH. Moreover, it was further demonstrated that a naphthoquinone polymer could oxidize NADH directly without diaphorase present .…”

Copper nanoparticles suitable for bifunctional cholesterol oxidation reaction: harvesting energy and sensor

“…Minteer's team reported a cholesterol biofuel cell using the cholesterol enzyme dehydrogenase (ChDH) in the bioanode with the redox polymer FcMe 2 -LPEI and the bilirubin enzyme oxidase (BOx) in the cathode linked to MWCNT-modified with anthracene, both in a single compartment. They reported 0.59 V OCV, 101 µA cm −2 and 20.3 µW cm −2 of current and power density respectively, at pH 7.5 and 5 mM Chol a of [46]. Sekretaryova reported a cholesterol self-powered biosensor using the enzyme cholesterol oxidase (ChOx) with phenothiazine in the anode and the enzyme ChOx with Prussian blue in the cathode; the cell had a single compartment and operated at pH 6.8 with 0.1 M KCl and 1% (w/w) Triton X-100 using different Chol concentrations.…”

Enzymatic Fuel Cells: Towards Self-Powered Implantable and Wearable Diagnostics

“…This novel biosensor showed high specificity to cholesterol 26 mA mM −1 cm −2 , with a dynamic range of 0.15–4.1 mM. Recently, Minteer et al developed an EFC cholesterol sensor made of a cholesterol dehydrogenase anode coupled with a bilirubin oxidase cathode [ 74 ]. In particular, bilirubin oxidase was entrapped in a dimethyl-ferrocene LPEI polymer and diaphorase was used as a mediator, while the bioanode was prepared by immobilising the enzyme onto anthracene-modified multi-walled carbon nanotubes drop-cast on buckypaper.…”