Metabolic monitoring by using the rate of change of NAD(P)H fluorescene

Changes in Autofluorescence Level of Live and Dead Cells for Mouse Cell Lines

Label-free characterization of cell subpopulations is a very promising biomedical approach. Nowadays, there are several label-free methods based on different physical properties such as size, density, stiffness, etc. allowing the characterization of biological objects. However, fluorescence properties are the most suitable feature for the label-free study of tissue and cells. Understanding the autofluorescence level peculiarities of normal and pathological / live and dead cells can become a helpful tool for cells' metabolic activity, viability evaluation, and diagnostics of a number of diseases. In this study, we applied a series of mouse cell lines (RAW 264.7 - macrophages, L929 - fibroblasts, C2C12 - myoblasts, and B16-F10 - melanoma) to compare cell autofluorescence of live and dead cells under 488 nm laser excitation and found the difference between their autofluorescence depending on a cell state and type.

Electrochemical evaluation of cellular physiological status under stress in Escherichia coli with the rpoS-lacZ reporter gene

We developed an electrochemical detection method for evaluating cellular physiological status based on the stringent response as a means to monitor cell viability. A reporter plasmid was constructed by inserting the beta-galactosidase gene (lacZ) under the control of the rpoS promoter, and then used to transform E. coli cells. Electrochemical responses from the products catalyzed by beta-galactosidase expressed by these E. coli cells were detected using the chronoamperometric technique in a nondestructive manner. Comparisons of response currents between the relA-positive strain and relA-negative strain revealed that increases in these currents were caused by the stringent response due to the stressful alcoholic environment, and thus as a model of stressful cultivating conditions. The current was proportional to the beta-galactosidase activity assayed by a conventional method that required the destruction of cells. The cellular physiological status, which depends on the stringent response as a viability marker, therefore, could then be evaluated online with a current using the rpoS-lacZ reporter gene in the relA-positive strain without pretreatment.

Monitoring aerobic sludge digestion by online scanning fluorometry

With sludge samples from two wastewater treatment plants, batch experiments of aerobic sludge digestion were conducted under different dissolved oxygen (DO) and solids concentrations. A fluorometer capable of online excitation and emission scanning was used to monitor the digestion process. Three major fluorescence peaks were observed. The peak at excitation/emission maxima of 290/350 nm was attributed to the fluorescence of proteinaceous materials in the sludge, with tryptophan residues being the primary contributor. The sources for the other two peaks (at 370/430 nm and 430/510 nm) remain unknown. The well-known biological fluorescence from reduced nicotinamide adenine dinucleotides (NADH and NADPH), at excitation/emission maxima of 340/460 nm, was found very weak in the aerobic digestion systems studied. It was buried under the broad peak at 370/430 nm and was detectable only in the early stage of the experiment that had the highest solids loading (at 4.8%) and was operated under low DO (0.2-1.0mg/L) conditions. On the other hand, the profile of the protein fluorescence (PF) correlated well with that of the volatile solids (VS) reduction in all the experiments. A semi-empirical exponential decay function was developed, which described well the profiles of both normalized VS and normalized PF. The feasibility of following the real-time performance of aerobic sludge digestion by monitoring PF was clearly demonstrated.

In-situ-fluorescence-probes: a useful tool for non-invasive bioprocess monitoring

Optical sensors appear to be very promising for different applications in modern biotechnology. They offer the possibility to interface all the well known optical analysis techniques to bioprocesses via fiber optical cables. Thus, high sophisticated and sensitive optical analysis techniques can be coupled to a bioprocess via these light signal transporting fibers. A wide variety of sensor types for application in biotechnology has been described. Normally these sensors are non-invasive and the response times are nearly instantaneous. In particular, the use of glass fiber technology makes these sensors small, robust and reduces their costs.

Light-induced changes of NADPH fluorescence in isolated chloroplasts: a spectral and fluorescence lifetime study

Isolated chloroplasts show a light-induced reversible increase in blue-green fluorescence (BGF), which is only dependent on NADPH changes. In the present communication, we report a time-resolved and spectral analysis of this BGF in reconstituted chloroplasts and intact isolated chloroplasts, in the dark and under actinic illumination. From these measurements we deduced the contribution of the different forms of NADPH (free and bound to proteins) to the light-induced variation of BGF and conclude that this variation is due only to the redox change of the NADP pool. A simple model estimating the distribution of NADPH between the free and bound form was designed, that explains the differences measured for the BGF of reconstituted chloroplasts and intact chloroplasts. From the decay-associated spectra of the chloroplast BGF, we also deduced the participation of flavins to the green peak of chloroplast fluorescence emission spectrum, and the existence of excitation energy transfer from proteins to bound NADPH in chloroplasts. In addition, we re-examined the use of chloroplast BGF as a quantitative measure of NADPH concentration, and confirmed that chloroplast BGF can be used for non-destructive, continuous and probably quantitative monitoring of light-induced changes in NADP redox state.