Over the past two decades, there has been an increasing trend towards miniaturization of both biological and chemical sensors and their integration with miniaturized sample pre-processing and analysis systems. These miniaturized lab-on-chip devices have several functional advantages including low cost, their ability to analyze smaller samples, faster analysis time, suitability for automation, and increased reliability and repeatability. Electrical based sensing methods that transduce biological or chemical signals into the electrical domain are a dominant part of the lab-on-chip devices. A vital part of any electrochemical sensing system is the reference electrode, which is a probe that is capable of measuring the potential on the solution side of an electrochemical interface. Research on miniaturization of this crucial component and analysis of the parameters that affect its performance, stability and lifetime, is sparse. In this paper, we present the basic electrochemistry and thermodynamics of these reference electrodes and illustrate the uses of reference electrodes in electrochemical and biological measurements. Different electrochemical systems that are used as reference electrodes will be presented, and an overview of some contemporary advances in electrode miniaturization and their performance will be provided.
Silk fibroin-derived polypeptides (FDPs) are polypeptides resulting from the enzymatic separation of the hydrophobic crystalline (C
p
) and hydrophilic electronegative amorphous (C
s
) components of silk fibroin (SF). The role of these polypeptides in promoting the nucleation of hydroxyapatite (HA) has been previously investigated, yet is still not fully understood. Here we study the potential of HA mineralization via FDPs incorporated at 1:10, 1:2 and 1:1 in a plastically compressed (PC) and dense collagen (DC) scaffold. Scaffolds were immersed in simulated body fluid (SBF) at physiological conditions (pH = 7.4, 37°C) to promote biomineralization. The effect of C
s
and C
p
to promote HA nucleation was investigated at different time points, and compared to pure DC scaffolds. Characterization of C
s
and C
p
fragments using Liquid Chromatography–Mass Spectrometry (LCMS) showed little difference in the amino acid composition of the FDPs. Results obtained
in vitro
using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM) X-Ray Diffraction (XRD) and mass analysis showed little difference between scaffolds that incorporated C
s
, C
p
, and DC hydrogels. These results demonstrated that silk FDPs incorporation are not yet suitable to promote HA nucleation
in vivo
without further refining the collagen-FDP system.
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