Real-time monitoring using fibre optics

Real-time monitoring using fibre-optics... 

The application of near-IR spectroscopy for real-time monitoring of glucose, lactic acid, acetic acid and biomass in liquid cultures of microorganisms of the genera Lactobacillus and Staphylococcus has been recently published [76]. The NIR spectrum acquired by the optical-fibre probe immersed in the culture is exploited using a partial least squares (PLS) calibration step, a classical method for IR techniques. 

Molecular beacons (MBs) are hairpin-shaped oligonucleotides that report the presence of specific nucleic acids. The MBs have been immobihzed by Tan and co-workers [27] onto ultrasmall optical fibre probes through avidin-biotin binding. The MB-DNA biosensor detected its target DNA molecules, in real time, with selectivity for a single base-pair mismatch. This MB-DNA-biosensor was used by Perlette and Tan [28] for real-time monitoring of mRNA-DNA hybridization inside a living cell. 

Experimentally the technique is simple since the sample may be irradiated from time to time and the emission intensity measured by a photomultiplier over a period of tens of seconds (Lange et al, 1998). However, these studies confirmed the limited usefulness of CRL alone for real-time monitoring since the emission is significant only in the glassy state, so this technique cannot detect the gel point for the majority of networks. When combined with other luminescence methods it has potential use because it is independent of the atmosphere and is readily adaptable to fibre-optics. 

Applications of the fibre optics transmittance or ATR probe are in quality control, reaction monitoring, skin analysis, goods-in checking, analysis at high and low temperature, radioactive or sterile conditions, and hazardous environments. Applications of the reflectance probe are for turbid liquids, powders, surface coatings, textiles, etc. By using an on-line remote spectrophotometer, real-time information is gathered about a chemical process stream (liquids, films, polymer melts, etc.), as often as necessary and without the need to collect samples. This determines more reliable process control. Remote spectroscopy costs less to maintain and operate than traditional techniques. Fernando et al. [48] have compared different types of optical fibre sensors to monitor the cure of an epoxy resin system. 

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