Abstract
Porous silicon (PSi) has been widely used as a biosensor over the last years due to its large surface area and its optical properties. Most PSi biosensors consist in close-ended porous layers, and, because of the diffusion-limited infiltration of the analyte, they lack sensitivity and speed of response. In order to overcome these shortcomings, PSi membranes (PSiMs) have been fabricated using electrochemical etching and standard microfabrication techniques. In this work, PSiMs have been used for the optical detection of Bacillus cereus lysate. Before detection, the bacteria are selectively lysed by PlyB221, an endolysin encoded by the bacteriophage Deep-Blue targeting B. cereus. The detection relies on the infiltration of bacterial lysate inside the membrane, which induces a shift of the effective optical thickness. The biosensor was able to detect a B. cereus bacterial lysate, with an initial bacteria concentration of 106 colony forming units per mL (CFU/mL), in less than 10 min. This work also demonstrates the selectivity of the lysis before detection. Not only does this detection platform enable the fast detection of bacteria, but the same technique can be extended to other bacteria using selective lysis.
Highlights
A biosensor allows the fast detection and quantification of a biological analyte, without preenrichment steps
The biosensing platform operates in two steps: a first step is the selective lysis of the targeted bacteria by an endolysin in a vial; and secondly, the optical monitoring of the bacterial lysate filtering through a PSi membranes (PSiMs) using the reflective interferometric Fourier transform spectroscopy (RIFTS) method. We demonstrate this concept with a selective optical detection of B. cereus lysate in PBS using the recently characterized PlyB221 endolysins, encoded by the Deep-Blue phage targeting B. cereus [26]
The effective optical thickness of Porous Silicon is strongly dependent on its refractive index
Summary
A biosensor allows the fast detection and quantification of a biological analyte, without preenrichment steps. The biological element frequently takes the form of a bioreceptor, which is bound to the surface of the transducer This binding requires several steps of surface modification or functionalization, which can be complex, time-consuming and/or expensive. Functionalization can shorten the lifespan of the biosensor and often puts heavy requirements on the storage conditions These bottlenecks can be avoided by adding the biological element into the sample volume instead of binding it to the transducer. Among these biological elements are endolysins: produced by bacteriophages or bacterial cells, they have the capability to digest the cell wall of specific bacterial strains. They have proven to be powerful selectivity means for the detection of bacteria [2,3,4]
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