Gravity-assisted distillation on a chip: Fabrication, characterization, and applications.

Distillation is widely used in industrial processes and laboratories for sample pre-treatment. The conventional apparatus of flash distillation is composed of heating source, distilling flask, condenser, and receiving flask. As disadvantages, this method shows manual and laborious analyses with high consumption of chemicals. In this paper, all these limitations were addressed by developing a fully integrated microscale distiller in agreement with the apparatus of conventional flash distillation. The main challenge facing the distillation miniaturization is the phase separation since surface forces take over from the gravity in microscale channels. Otherwise, our chip had ability to perform gravity-assisted distillations because of the somewhat large dimensions of the distillation chamber (roughly 900 µL) that was obtained by 3D-printing. The functional distillation units were integrated into a single device composed of polydimethylsiloxane (PDMS). Its fabrication was cost-effective and simple by avoiding the use of cleanroom and bonding step. In addition to user-friendly analysis and low consumption of chemicals, the method requires cost-effective instrumentation, namely, voltage supply and analytical balance. Furthermore, the so called distillation-on-a-chip (DOC) eliminates the use of membranes and electrodes (usually employed in microfluidic desalinations reported in the literature), thus avoiding drawbacks such as liquid leakage, membrane fouling, and electrode passivation. The DOC promoted desalinations at harsh salinity (NaCl 600.0 mmol L-1) with high throughput and salt removal efficiency (roughly 99%). Besides, the method was used for determination of ethanol in alcoholic beverages to show the potential of the approach toward quantitative purposes.

Optical paper-based sensor for ascorbic acid quantification using silver nanoparticles.

In this paper, we demonstrate for the first time the use of silver nanoparticles (AgNPs) for colorimetric ascorbic acid (AA) quantification in a paper-based sensor. This device is constituted by spot tests modified with AgNPs and silver ions bordered by a hydrophobic barrier which provides quantitative and fast analysis of AA. In addition, this device is employed as point-of-care monitoring using a unique drop of the sample. AgNPs paper-based sensor changed from light yellow to gray color after the addition of AA due to nanoparticle growth and clusters formation. The color intensities were altered as a function of AA concentration which were measured by either a scanner or a homemade portable transmittance colorimeter. Under the selected measurement conditions, results presented limit of detection which was comparable to analytical laboratory-based methodologies. In addition, the sensitivity of our sensor was comparable to the standard titration method when real samples were investigated.

An integrated platform for gas-diffusion separation and electrochemical determination of ethanol on fermentation broths.

An integrated platform was developed for point-of-use determination of ethanol in sugar cane fermentation broths. Such analysis is important because ethanol reduces its fuel production efficiency by altering the alcoholic fermentation step when in excess. The custom-designed platform integrates gas diffusion separation with voltammetric detection in a single analysis module. The detector relied on a Ni(OH)2-modified electrode. It was stabilized by uniformly depositing cobalt and cadmium hydroxides as shown by XPS measurements. Such tests were in accordance with the hypothesis related to stabilization of the Ni(OH)2 structure by insertion of Co(2+) and Cd(2+) ions in this structure. The separation step, in turn, was based on a hydrophobic PTFE membrane, which separates the sample from receptor solution (electrolyte) where the electrodes were placed. Parameters of limit of detection and analytical sensitivity were estimated to be 0.2% v/v and 2.90 µA % (v/v)(-1), respectively. Samples of fermentation broth were analyzed by both standard addition method and direct interpolation in saline medium based-analytical curve. In this case, the saline solution exhibited ionic strength similar to those of the samples intended to surpass the tonometry colligative effect of the samples over analyte concentration data by attributing the reduction in quantity of diffused ethanol vapor majorly to the electrolyte. The approach of analytical curve provided rapid, simple and accurate analysis, thus contributing for deployment of point-of-use technologies. All of the results were accurate with respect to those obtained by FTIR method at 95% confidence level.