Porous Silicon‐Based Optical Microsensors for Volatile Organic Analytes: Effect of Surface Chemistry on Stability and Specificity

Abstract

Sensing of the volatile organic compounds (VOCs) isopropyl alcohol (IPA) and heptane in air using sub-millimeter porous silicon-based sensor elements is demonstrated in the concentration range 50-800 ppm. The sensor elements are prepared as one-dimensional photonic crystals (rugate fi lters) by programmed electrochemical etch of p + + silicon, and analyte sensing is achieved by measurement of the wavelength shift of the photonic resonance. The sensors are studied as a function of surface chemistry: ozone oxidation, thermal oxidation, hydrosilylation (1-dodecene), electrochemical methylation, reaction with dicholorodimethylsilane and thermal carbonization with acetylene. The thermally oxidized and the dichlorodimethylsilane-modifi ed materials show the greatest stability under atmospheric conditions. Optical microsensors are prepared by attachment of the porous Si layer to the distal end of optical fi bers. The acetylated porous Si microsensor displays a greater response to heptane than to IPA, whereas the other chemical modifi cations display a greater response to IPA than to heptane. The thermal oxide sensor displays a strong response to water vapor, while the acetylated material shows a relatively weak response. The results suggest that a combination of optical fi ber sensors with different surface chemistries can be used to classify VOC analytes. Application of the miniature sensors to the detection of VOC breakthrough in a full-scale activated carbon respirator cartridge simulator is demonstrated.

Bioconjugate functionalization of thermally carbonized porous silicon using a radical coupling reaction

“…2b) thereby showing that the carbonized surface retains sufficient optical transparency to allow optical biosensing. Although thermal carbonization can leave black, optically dense carbonaceous deposits that completely obscure the optical interference spectrum, prior studies have shown that when the reaction is carried out at moderate temperatures (500 °C, as in the present study) the deposit is sufficiently thin to yield adequate optical transparency while retaining the desired chemical stability of a silicon carbide-like surface 23,56…”

Porous silicon micro- and nanoparticles for printed humidity sensors

“…[33][34][35] In addition, the surface chemistry of PSi can be modified easily. [36][37][38] Among the different surface chemistries, thermally carbonized PSi displays a highly increased electrical conductivity, 39,40 which enables, along with the possibility of fabricating nano-and microparticles, the preparation of PSi-based solution-processable inks needed for making printable devices. In the current study, the feasibility of PSi particles for printed humidity sensor production is explored.…”

Responsive photonic crystal for the sensing of environmental pollutants

“…The ability of the double-stack structure to discriminate water vapor and VOCs was quantified for four different VOCs: toluene, dimethyl methylphosphonate (DMMP), heptane and ethanol over a range of RH values (25% < RH < 75%). They also designed an optical microsensor by attaching the porous Si layer to the distal end of optical fibers [30]. In this work, they combined surface chemistries, such as ozone oxidation, thermal oxidation, hydrosilylation (1-dodecene), electrochemical methylation, reaction with dicholorodimethylsilane and thermal carbonization with acetylene, to modify materials.…”