Search

A flow-injection analytical (FIA) system was developed for the determination of cholesterol concentrations based on enzymatic reactions that occurred in a cholesterol oxidase (CHOx)-immobilized, fused-silica capillary followed by electrochemical detection. The production of hydrogen peroxide from cholesterol in an enzymatic reaction catalyzed by CHOx was subsequently oxidized electrochemically at an electrode. Our FlA system demonstrated its cost-effectiveness and utility at an applied potential of 0.6 V (vs. Ag/AgCl), a flow rate of 100 μL/min and, under optimal conditions, the resulting signal demonstrated a linear dynamic range from 50 μM to 1.0 mM with a limit of detection (LOD) of 12.4 μM, limit of quantification (LOQ) of 44.9 μM, and the coefficient of variation of 5.17%. In addition, validation of our proposed system using a reference HDL-cholesterol kit used for clinical diagnosis suggested our FIA system was comparable to commercial kits for the determination of the cholesterol incorporation amount in various aqueous liposomal suspensions. These good analytical features achieved by FIA could make the implementation of this methodology possible for on-line monitoring of cholesterol in various types of samples.

In this study we developed a novel approach, using in-capillary formation of polymer/surfactant complexes (IPSC)–assisted reversed-migration MEKC (RM-MEKC), for the analysis of neutral steroids. This process involved two sequential events: in-capillary polymer/surfactant complexes formation during sample preconcentration, followed by IPSC separation. The procedure began with a polymer-filled capillary. Initially, on-line preconcentration of the sample was performed at the sample plug. Meanwhile, free surfactants migrated to interact with polymers, forming polymer–surfactant complexes. Analytes were then kinetically partitioned between the mixed phases (micelles and polymer–SDS complexes). Sodium dodecyl sulfate (SDS) and poly(N-isopropylacrylamide) (PNIPAAm) were employed as pseudo-stationary phases (PSPs). This system allowed the successful separation of five steroids (testosterone, hydrocortisone 21-acetate, dexamethasone, prednisolone, hydrocortisone) in acetate buffer and the determination of urinary free hydrocortisone; it also exhibited excellent performance for sample on-line concentration. The limit of detection for hydrocortisone was 20.98 ng/mL (R2=0.9995). The polymer size, concentrations, end-group charges, and SDS concentrations were evaluated. This IPSC/RM-MEKC system, which can be adopted in commercial CE instruments, is easy to operate, suitable for combination with several sample preconcentration options, sensitive, robust, and environmentally sustainable. We suspect that such systems might have potential applications in clinical analyses and in microanalytical devices.

In recent years, personalized fabrication has attracted much attention due to the greatly improved accessibility of consumer-level 3D printers. However, 3D printers still suffer from the relatively long production time and limited output size, which are undesirable for large-scale rapid-prototyping. Zometool, which is a popular building block system widely used for education and entertainment, is potentially suitable for providing an alternative solution to the aforementioned scenarios. However, even for 3D models of moderate complexity, novice users may still have difficulty in building visually plausible results by themselves. Therefore, the goal of this work is to develop an automatic system to assist users to realize Zometool rapid prototyping with a specified 3D shape. Compared with the previous work [Zimmer and Kobbelt 2014], our method may achieve the ease of assembly and economic usage of building units since we focus on generating the Zometool structures through a higher level of shape abstraction.