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Optical biosensor to detect the concentration of Escherichia coli using a hyperspectral microscope

In technology, a sensor is a system that detects changing events of an environment in the form of electromagnetic signals and transmits that information to a reader device. It has to be adaptable to the environment in order to yield the best performance in recognizing which signals to pass and which to disregard. A biosensor is an analytical system modified for the detection of biological substances such as microorganisms or physicochemical alterations within a biological environment. The main features of biosensors are their stability in the environment, sensitivity in signal detection and capability of transmitting the data in an accessible way for further analysis.

An example of a biosensor could be fluorescent probes that bind to a specific target and upon a controllable condition such as laser illumination or pH change, the fluorescent signal could indicate measurable information about the subject under study. In life science, fluorescent probes are used as biosensors for diagnosis purposes. Since most of them are focused on the first biological window, the shortcoming of those probes has a minimal depth penetration of their IN VIVO studies.

Fig. 1 | Normalized photoluminescence intensity dependence for different concentrations of bacterial solutions observed in situ with SAM-based architectures. The samples were rinsed after 30 min of exposure to the bacteria. The results are shown without subtracting the PBS-related signal.

Here we present a research group that has developed photoluminescence-based quantum semiconductor biosensors for the detection of a bacterial infection. Depending on two different antibody conjugations, these biosensors could detect the E. coli within less than 120 minutes of the bacterial exposure1. The collection of photoluminescence was done with the IMA™ hyperspectral microscope. Optical microscopy images were acquired to estimate the density of bacteria on the samples over a period of up to 5 hours.

With the IMA™ hyperspectral microscope, it was possible to detect the E. coli using photoluminescence from GaAs/Al0.33Ga0.67As microstructures as the system provides spectral and spatial resolution. A series of experiments with photoluminescence measurements with different concentrations in situ CFU/ml of L. Lactis has been done (see figure 1). With the use of a filter wheel, the observation of the emission spectra of a specific fluorophore with a broad width of emission can be achieved. The IMA™ allows fast acquisition with the motorized focus for any application requiring high spectral resolution since it has the advantage of detecting monochromatic images of the entire field of view over time so it does not lose spectral information.

[1] Duplan, V., Frost, E., & Dubowski, J. J. (2011). A photoluminescence-based quantum semiconductor biosensor for rapid in situ detection of Escherichia coli. Sensors and Actuators B: Chemical, 160(1), 46–51.


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