Aqueous synthesis of CdTe quantum dot as biological fluorescent probe for monitoring methyl parathion by fluoro-immunosensor

Bioconjugation of quantum dots (QDs) provide high resolution in biological fluorescent labelling as a result of physical and optical properties of QDs. This intrinsic property of QDs can be made use of for sensitive detection of target analytes including food and environmental monitoring. In this investigation, we report the bioconjugation of thiol stabilized CdTe QD for the sensitive detection of methyl parathion (MP) at picogram level. The specificity in the analysis was attributed by highly specific competitive immunological reactions between free MP and CdTe QD bioconjugated MP (MP-BSA-CdTe) for immobilized anti-MP IgY antibodies in a simple flow injection system. We also report the possible resonance energy transfer phenomenon as a result of nanobiomolecular interaction obtained through the bioconjugation of CdTe QD with protein bovine serum albumin (BSA). This has resulted in a significant change in the photo-absorption of CdTe QD, which can be made use for future nanosensor development

Large eddy simulation of partially premixed turbulent combustion

Imperial Users onl

HIV-1 reverse transcriptase mutations that confer decreased in vitro susceptibility to anti-RT DNA aptamer RT1t49 confer cross resistance to other anti-RT aptamers but not to standard RT inhibitors

RNA and DNA aptamers specific for HIV-1 reverse transcriptase (RT) can inhibit reverse transcription in vitro. RNA aptamers have been shown to potently block HIV-1 replication in culture. We previously reported mutants of HIV-1 RT with substitutions N255D or N265D that display resistance to the DNA aptamer RT1t49. Variant viruses bearing these mutations singly or in combination were compromised for replication. In order to address the wider applicability of such aptamers, HIV-1 RT variants containing the N255D, N265D or both (Dbl) were tested for the extent of their cross-resistance to other DNA/RNA aptamers as well as to other RT inhibitors. Both N265D and Dbl RTs were resistant to most aptamers tested. N255D mutant displayed mild resistance to two of the DNA aptamers, little change in sensitivity to three and hypersensitivity to one. Although all mutants displayed wild type-like ribonuclease H activity, their activity was compromised under conditions that prevent re-binding. This suggests that the processivity defect caused by these mutations can also affect RNase H function thus contributing further to the replication defect in mutant viruses. These results indicate that mutants conferring resistance to anti-RT aptamers significantly affect many HIV-1 RT enzymatic activities, which could contribute to preventing the development of resistance in vivo. If such mutations were to arise in vivo, our results suggest that variant viruses should remain susceptible to many existing anti-RT inhibitors. This result was tempered by the observation that NRTI-resistance mutations such as K65R can confer resistance to some anti-RT aptamers

Analysis and Design of Analog Front-end Circuitry for Avalanche Photodiodes (APD) and Silicon Photo-multipliers (SiPM) in Time-of-flight Applications

This thesis reports the analysis and design of analog front-end circuitry for reading out signals from avalanche photodiodes (APD) or silicon photomultiplier (SiPM) in time-of-flight (ToF) applications. An integrated circuit was designed using AMS SiGe 0.35 um BiCMOS process. The chip measured 2 mm x 2 mm (2000 umx2000 um). The chip mainly contains the following circuits: an APD with photoactive area measuring 24 umx24 um, an SiPM with 8x8 APDs with 236 k ohm quench resistors, a transimpedance amplifier (TIA), a comparator and a R-2R digital to analog converter (DAC). The TIA is based on the shunt-shunt feedback topology. The TIA gain can be digitally set using two input bits to range from -0.9 k ohm to -14.44 k ohm with a bandwidth ranging from 93 MHz to 113 MHz. Photodetector capacitance on TIA input reduces the bandwidth. The maximum positive input current dynamic range of the TIA is 294 uA. The TIA consumes a power of 7.1 mW. The comparator has a maximum speed of 265 MHz with input sensitivity down to 50 uV and consumes about 6.6 mW of power. The R-2R DAC has a 10-bit resolution with maximum differential nonlinearity (DNL) and integral nonlinearity (INL) of -0.14 LSB and -0.09 LSB respectively with no load. Design considerations for all the blocks are given and simulation results are compared to hand calculations. The TIA, comparator and DAC are connected as a system and the simulation is functional. Using this system to implement a time-of-flight LiDAR (light detection and ranging), a range resolution down to 1.2 m (3.9 ft) can be achieved with photodetector capacitance of 0.1 pF