Passive direct methanol fuel cells acting as fully autonomous electrochemical biosensors: Application to sarcosine detection

This work describes an innovative electrochemical biosensor that advances its autonomy toward an equipment-free design. The biosensor is powered by a passive direct methanol fuel cell (DMFC) and signals the response via an electrochromic display. Briefly, the anode side of the DMFC power source was modified with a biosensor layer developed using molecularly imprinted polymer (MIP) technology to detect sarcosine (an amino acid derivative that is a potential cancer biomarker). The biosensor layer was anchored on the surface of the anode carbon electrode (carbon black with Pt/Ru, 40:20). This was done by bulk radical polymerization with acrylamide, bis-acrylamide, and vinyl phosphonic acid. This layer selectively interacted with sarcosine when integrated into the passive DMFC (single or multiple, in a stack of 4), which acted as a transducer element in a concentration-dependent process. Serial assembly of a stack of hybrid DMFC/biosensor devices triggered an external electrochromic cell (EC) that produced a colour change. Calibrations showed a concentration-dependent sarcosine response from 3.2 to 2000 µM, which is compatible with the concentration of sarcosine in the blood of prostate cancer patients. The final DMFC/biosensor-EC platform showed a colour change perceptible to the naked eye in the presence of increasing sarcosine concentrations. This colour change was controlled by the DMFC operation, making this approach a self-controlled and self-signalling device. Overall, this approach is a proof-of-concept for a fully autonomous biosensor powered by a chemical fuel. This simple and low-cost approach offers the potential to be deployed anywhere and is particularly suitable for point-of-care (POC) analysis.The authors acknowledge the financial support of EU-Horizon 2020 (Symbiotic, FET-Open, GA665046), and from national funds from FCT - Fundação para a Ciência e a Tecnologia, I.P., in the scope of the projects LA/P/0037/2020, UIDP/50025/2020, UIDB/50025/2020 and UID/EMS/00532/2019. Nádia Ferreira (SFRH/BD/122955/2016), Liliana Carneiro (SFRH/BD/122954/2016), and Ana Carolina Marques (SFRH/BD/115173/2016) acknowledge Fundação para a Ciência e Tecnologia (FCT) for financial support.info:eu-repo/semantics/publishedVersio

Molecular velocity auto-correlation of simple liquids observed by NMR MGSE method

The velocity auto-correlation spectra of simple liquids obtained by the NMR method of modulated gradient spin echo show features in the low frequency range up to a few kHz, which can be explained reasonably well by a $t^{-3/2}$ long time tail decay only for non-polar liquid toluene, while the spectra of polar liquids, such as ethanol, water and glycerol, are more congruent with the model of diffusion of particles temporarily trapped in potential wells created by their neighbors. As the method provides the spectrum averaged over ensemble of particle trajectories, the initial non-exponential decay of spin echoes is attributed to a spatial heterogeneity of molecular motion in a bulk of liquid, reflected in distribution of the echo decays for short trajectories. While at longer time intervals, and thus with longer trajectories, heterogeneity is averaged out, giving rise to a spectrum which is explained as a combination of molecular self-diffusion and eddy diffusion within the vortexes of hydrodynamic fluctuations.Comment: 8 pages, 6 figur

Fuel cells operating as an immunosensor for cancer biomarker screening

This work presents the first integration of antibodies into one of the electrodes of a passive direct methanol fuel cell (DMFC) to create an autonomous immunosensor for cancer antigen 15–3 (CA15-3). The anode of the fuel cell was first made of carbon cloth with carbon black, platinum and ruthenium nanoparticles and then modified with anti-CA15-3, while the cathode was made of carbon cloth with carbon black and platinum nanoparticles. This hybrid DMFC (hDMFC), which works as an immunosensor, was fed with dilute methanol to generate a concentration-dependent current. The hDMFC device was calibrated in different media (buffer and serum), by incubating increasing concentrations of CA15-3 standard solutions, ranging from 47 to 750 U/mL. The linear response ranged from 188 to 563 U/mL, and the limit of detection (LoD) was 39.8 U/mL. The selectivity of the biosensor was also evaluated with competing cancer biomarkers, such as carcinoembryonic antigen (CEA), and cancer antigen 125 (CA-125), as well as with other compounds normally present in blood plasma (ascorbic acid, glucose, uric acid and urea), adjusted to the normal range of concentrations in serum. The results obtained indicate good selectivity of the immunosensor in the fuel cell. In general, the immunosensor showed a good response considering its integration into a passive DMFC. It is a good sensor for point-of-care (PoC) diagnosis because it has a good performance in human serum and, most importantly, it pursues electrical autonomy.info:eu-repo/semantics/publishedVersio