A new microfluidic device with liquid-droplet merging and droplet storage functions for the controlled release of drugs from microcapsules is reported. A switching channel is designed and integrated within the microfluidic device, facilitating the generation and capturing of uniform droplets by the storage chambers. The drug model is the MnCO 3 microparticle, which is encapsulated by a microcapsule and fabricated using a simple layer-by-layer nanoassembly process. The merging function is used for dynamically adding the control solution into the droplets, which contain drugs within the microcapsules (DWlCs) and water. The storage chambers are used for collecting DWlCs-laden droplets so that the controlled-drug release in specific droplets can be monitored for an extended period of time, which has been experimentally implemented successfully. This technology could offer a promising technical platform for the long-term observation and studies of drug effects on specific cells in a controlled manner, which is especially useful for single cell analysis. V C 2013 AIP Publishing LLC.
New determination scheme of p-aminophenol by using MnO 2 as a preoxidant is demonstrated in this work. In the flow injection system, the p-aminophenol is oxidized to quinoneimine by MnO 2 at up-stream, which can be detected at a suitable reductive potential. After optimization, the linear range of PAP is started from 1 mM to 30 mM (R 2 ¼ 0.999), the estimated detection limit (S/N ¼ 3) is 0.28 mM. Two real samples are studied and excellent recoveries are achieved by using standard addition method. The p-aminophenol (PAP) is a primary hydrolytic degradation product of acetaminophen (AC) [1], and AC is very widely used as analgesic and antipyretic drug to reduce fever, cough and cold. Moreover, p-aminophenol is very harmful for human body due to its structural similarity to aniline and phenol [2]. It is limited to a low level of 0.005% in the drug substance by the European Pharmacopoeia (Ph. Eur.) [3]. The PAP or PAP derivate compounds are common pollutants in effluents from cooking oil refineries, production of pesticides and herbicides, dyes and textiles, pharmaceuticals, pulp and paper, plastics, and detergent [4], because they are extremely toxic to aquatic life and impart a strong disagreeable taste to water [5]. Several researches have reported different PAP determination schemes including high performance chromatography (HPLC), capillary electrophoresis (CE) [6 -10], optical chemical sensors [11,12] and electrochemical sensor [13 -15]. Among the aforementioned schemes, the advantages of electrochemical scheme are low cost and less time consuming. Other applications of PAP are used as electroactive polymer film [16,17] in the determination of the ascorbic acid. But the poly-PAP film only shows the electroactive property in acid condition. In the neutral or alkaline condition, it is well known, the poly-PAP is accumulated onto electrode surface leading to the electrode inactivation and the hindrance of signal in further electroanalytical measurements. Thus, the determination of PAP in neutral or alkaline condition is very hard to avoid the formation of nonconductive film on the electrode surface. Some electrode surface cleaning schemes [18 -20] or chemical modified electrodes [13 -15] have been reported to solve this problem. However, the aforementioned electrode cleaning schemes are not convenient for further application and the pulse cleaning scheme may damage the electrode surface either.In this work, the MnO 2 was modified on a dummied upstream electrode as a preoxidant to selective oxidation of the PAP. Subsequently, the oxidized product is detected by the down-stream electrode. This simple scheme avoids the polymerization effect of the PAP with direct oxidative method. Two surface water samples collected from local pond and field were adopted as real samples. The flow injection analysis (FIA) coupled with MnO 2 modified electrode is used in PAP determination without enzyme modification, complicated sample treatment procedures and expensive electrode materials.The solid line of Figure 1A shows a ...
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