Jonathan Rasson

Lytic enzymes as selectivity means for label-free, microfluidic and impedimetric detection of whole-cell bacteria using ALD-Al2O3 passivated microelectrodes

Point-of-care (PoC) diagnostics for bacterial detection offer tremendous prospects for public health care improvement. However, such tools require the complex combination of the following performances: rapidity, selectivity, sensitivity, miniaturization and affordability. To meet these specifications, this paper presents a new selectivity method involving lysostaphin together with a CMOS-compatible impedance sensor for genus-specific bacterial detection. The method enables the sample matrix to be directly flown on the polydopamine-covered sensor surface without any pre-treatment, and considerably reduces the background noise. Experimental proof-of-concept, explored by simulations and confirmed through a setup combining simultaneous optical and electrical real-time monitoring, illustrates the selective and capacitive detection of Staphylococcus epidermidis in synthetic urine also containing Enterococcus faecium. While providing capabilities for miniaturization and system integration thanks to CMOS compatibility, the sensors show a detection limit of ca. 10(8) (CFU/mL).min in a 1.5 μL microfluidic chamber with an additional setup time of 50 min. The potentials, advantages and limitations of the method are also discussed.

Vapour sensitivity of an ALD hierarchical photonic structure inspired by Morpho

The unique architecture of iridescent Morpho butterfly scales is known to exhibit different optical responses to various vapours. However, the mechanism behind this phenomenon is not fully quantitatively understood. This work reports on process developments in the micro-fabrication of a Morpho-inspired photonic structure in atomic layer deposited (ALD) materials in order to investigate the vapour optical sensitivity of such artificial nanostructures. By developing recipes for dry and wet etching of ALD oxides, we micro-fabricated two structures: one combining Al2O3 and TiO2, and the other combining Al2O3 and HfO2. For the first time, we report the optical response of such ALD Morpho-like structures measured under a controlled flow of either ethanol or isopropyl alcohol (IPA) vapour. In spite of the small magnitude of the effect, the results show a selective vapour response (depending on the materials used).

Improved Stability of Porous Silicon in Aqueous Media via Atomic Layer Deposition of Oxides

In this work, porous silicon (PSi) samples were conformally coated with ultrathin films of aluminum oxide (Al2O3) and hafnium oxide (HfO2) using atomic layer deposition (ALD) to passivate their internal surface and improve their overall stability in aqueous media. Their porosity and optical properties were characterized before and after ALD treatment. The stability over time in aqueous media of the ALD passivated porous layers was then evaluated and compared to PSi layers oxidized at 800 °C (PSiO2), which is a treatment widely used in the literature for biosensing applications. The ALD oxide-covered samples performed equally to the oxidized PSi samples, but exhibited a higher mean refractive index, which results in a better contrast. These improved optical properties resulted in a signal exhibiting a significantly decreased noise. This in turn leads to a theoretical limit of detection improved by a factor 13 and 16 for PSi/Al2O3 and PSi/HfO2, respectively, compared to the standard PSiO2. This could thus r...