A signal detection technique utilising a 'lock-in' architecture using the second-order harmonic frequency (2 v c ) applicable to portable opticalbiosensor systems is presented. The properties of frequency synthesis and filtering techniques are used to detect a weak signal concealed in intense background noise, such as thermal noise, 1/f noise and shot noise. Using the 2 v c lock-in, the main signal of interest keeps away from the influence of the 1/f noise, providing a much higher dynamic reserve. In this work, a portable biosensor system using the 2 v c frequency detection technique is demonstrated. The technique further enhances the minimum detectable range of 20 dB compared to the conventional DC lock-in method under the same conditions.
1) In this study, poly (L-lactic acid) (PLLA) microparticles containing gemcitabine hydrochloride were prepared by a supercritical fluid process, called aerosol solvent extraction system (ASES), utilizing supercritical carbon dioxide as antisolvent. The influence of process parameters such as temperature, pressure, CO2 and solution flow rate, solution concentration, and feed ratio of drug to polymer on the morphology and characteristics of the microparticles was studied in detail. The gemcitabine-loaded microparticles exhibited a spherical shape with a smooth surface. The entrapment efficiency of gemcitabine increased with increasing temperature, solution concentration and CO 2 flow rate and with decreasing drug/polymer feed ratio. The maximum drug loading obtained from the ASES process was found to be about 11%. The ASES-processed PLLA microparticles containing gemcitabine showed a relatively high initial burst due to the presence of surface pores on the microparticles and the poor affinity between drug and polymer.
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