Fluorescent redox-dependent labeling of lipid droplets in cultured cells by reduced phenazine methosulfate

Single-molecule electrochemical imaging of 'split waves' in the electrocatalytic (EC') mechanism

We describe a single-molecule electrochemical imaging strategy to study the electrocatalytic (EC') mechanism. Using the fluorescent molecule ATTO647N at extremely low concentrations as the substrate, we confirmed its catalytic reduction to a nonfluorescent form in the presence of the mediator phenazine methosulfate (PMS) by imaging and counting fluorescent molecules. Conventional electrochemical current in cyclic voltammetry would not have allowed us to infer the existence of an EC' process or the PMS-mediated ATTO647N reduction. Additionally, we observed shifts in the catalytic reduction potential of ATTO647N at various mediator concentrations, which agree with the theoretical predictions by Savéant. Our work offers a new perspective on connecting single-molecule EC' behaviors with the conventional ensemble EC' mechanism, both practically and theoretically.

Fluorescent sensor based on pyrroloquinoline quinone (PQQ)-glucose dehydrogenase for glucose detection with smartphone-adapted signal analysis

A new nano-structured platform for fluorescent analysis using PQQ-dependent glucose dehydrogenase (PQQ-GDH) was developed, particularly using a smartphone for transduction and quantification of optical signals. The PQQ-GDH enzyme was immobilized on SiO₂ nanoparticles deposited on glass microfiber filter paper, providing a high load of the biocatalytic enzyme. The platform was tested and optimized for glucose determination using a wild type of the PQQ-GDH enzyme. The analysis was based on the fluorescence generated by the reduced form of phenazine methosulfate produced stoichiometrically to the glucose concentration. The fluorescent signals were generated at separate analytical spots on the paper support under wavelength (365 nm) UV excitation. The images of the analytical spots, dependent on the glucose concentration, were obtained using a photo camera of a standard smartphone. Then, the images were processed and quantified using software installed in a smartphone. The developed biocatalytic platform is the first step to assembling a large variety of biosensors using the same platform functionalized with artificial allosteric chimeric PQQ-dependent glucose dehydrogenase activated with different analytes. The future combination of the artificial enzymes, the presently developed analytical platform, and signal processing with a smartphone will lead to novel point-of-care and end-user biosensors applicable to virtually all possible analytes.

A Universal Multichannel Platform for Assembling Enzyme-Based Boolean Logic Gates

Concatenated enzyme-based Boolean logic gates activated with 5 chemical input signals were analyzed with a smartphone photo camera. Simultaneous detection of 32 input combinations was conveniently performed using enzyme-modified fiberglass sensing spots generating fluorescence with different intensities for the 0 and 1 binary outputs. The developed technology offers an easy readout method for multi-channel logic systems.