Human plasma and serum samples, including protein and peptide biomarkers, are subjected to preanalytical variations and instability caused by intrinsic proteases. In this study, we directly investigated the stability of peptide biomarkers by spiking an isotopically labeled peptide into human plasma and serum samples and then monitoring its time-dependent change. Fibrinogen peptide A (FPA) was used as a model substrate, and its degradation in a conventional serum and plasma either with citrate, heparin, or EDTA as the anticoagulant, or EDTA plus protease inhibitors (inhibited plasma), was measured using time-course MALDI-TOF MS analysis. The FPA and other peptides tested in this study vary in these samples. However, the peptides are most stable in the inhibited plasma followed by, in general order, EDTA plasma, citrate plasma, heparin plasma and serum, demonstrating the benefit of plasma versus serum, and protease inhibitors for biomarker stabilization. Kinetic analysis indicates that intrinsic peptidases cause an observed first-order Sequential Multiple-Step Reaction (SMSR) in digestion of the peptide. Modeling analysis of the SMSR demonstrates that step reactions differ in their kinetic rate constants, suggesting a significant contribution of the truncated end residue on the substrate specificity of the intrinsic peptidase(s). Our observations further show that synthetic peptides introduced into plasma as internal controls can also be degraded, and thus, their (in)stability as a preanalytical variable should not be overlooked.

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The ternary FePtSn alloy nanoparticles (NPs) were synthesized via a simple programmed microfluidic process, showing a great electrochemical performance in methanol oxidation reaction (MOR). The synthesis process exhibited convenient and spatial-temporal kinetics control of the NPs formation for a narrow size distribution, ultra-small (~2nm) and good dispersion features. The morphology, crystal structure and composition of FePtSn NPs were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD). FePtSn/C nanocatalyst ink could be further prepared by mixing the as-synthesized or annealed FePtSn NPs with carbon black powder and nafion. Their electrocatalytic performances were tested by the electrochemical work station. By contrast, the annealing treatment made more active sites exposed and facilitated the catalytic performance of FePtSn/C NPs. The electrochemical active surface areas (ECSAs, 42.8m2/g), catalytic activity (If: 588.1 mA/mg-Pt) and electrochemical durability of FePtSn/C nanocatalysts after annealing were greatly improved, comparing with as-synthesized samples and commercial Pt/C nanocatalysts for MOR. In addition, the onset potential of annealed FePtSn/C nanocatalysts was improved, much better than the commercial Pt/C nanocatalysts.

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