A microfluidic biosensor based on nucleic acid sequence recognition

The development of a generic semi-disposable microfluidic biosensor for the highly sensitive detection of pathogens via their nucleic acid sequences is presented in this paper. Disposable microchannels with defined areas for capture and detection of target pathogen RNA sequence were created in polydimethylsiloxane (PDMS) and mounted onto a reusable polymethylmethacrylate (PMMA) stand. Two different DNA probes complementary to unique sequences on the target pathogen RNA serve as the biorecognition elements. For signal generation and amplification, one probe is coupled to dye encapsulated liposomes while the second probe is coupled to superparamagnetic beads for target immobilization. The probes hybridize to target RNA and the liposome–target-bead complex is subsequently captured on a magnet. The amount of liposomes captured correlates directly to the concentration of target sequence and is quantified using a fluorescence microscope. Dengue fever virus serotype 3 sequences and probes were used as a model analyte system to test the sensor. Probe binding and target capture conditions were optimized for sensitivity resulting in a detection limit of as little as 10 amol L^–1 (10 pmol L^–1) . Future biosensors will be designed to incorporate a mixer and substitute the fluorescence detection with an electrochemical detection technique to provide a truly portable microbiosensor system.     

The use of stabilizers in the UV assay of ascorbic acid

Sodium thiosulphate (0.04%w/v) has been used to stabilize ascorbic acid in aqueous medium. The method has been used to assay ascorbic acid in commercial tablet preparations. It is very accurate, precise and reproducible. It compares favourably with official titrimetric method. The method is simple and can be adopted for the routine assay of ascorbic acid in single component tablet formulations.     

Use of nmr for quantitative analysis of pharmaceuticals

Many pharmaceutical preparations have been assayed successfully by the use of NMR. The method utilizes measurement of the area under selected signals of both test and standard samples by means of electronic integrators. The NMR method is simpler and faster than official methods of analysis although less precise.