Smart thin layer chromatography plate

On-Glass Integrated SU-8 Waveguide and Amorphous Silicon Photosensor for On-Chip Detection of Biomolecules: Feasibility Study on Hemoglobin Sensing

An optoelectronic, integrated system-on-glass for on-chip detection of biomolecules is here presented. The system’s working principle is based on the interaction, detected by a hydrogenated amorphous silicon photosensor, between a monochromatic light travelling in a SU-8 polymer optical waveguide and the biological solution under analysis. Optical simulations of the waveguide coupling to the thin-film photodiode with a specific design were carried out. A prototype was fabricated and characterized showing waveguide optical losses of about 0.6 dB/cm, a photodiode shot noise current of about 2.5 fA/Hz and responsivity of 495 mA/W at 532 nm. An electro-optical coupling test was performed on the fabricated device to validate the system. As proof of concept, hemoglobin was studied as analyte for a demonstration scenario, involving optical simulations interpolated with experimental data. The calculated detection limit of the proposed system for hemoglobin concentration in aqueous solution is around 100 ppm, in line with colorimetric methods currently on the market. These results show the effectiveness of the proposed system in biological detection applications and encourage further developments in implementing these kinds of devices in the biomedical field.

Multifunctional System-on-Glass for Lab-on-Chip applications

Lab-on-Chip are miniaturized systems able to perform biomolecular analysis in shorter time and with lower reagent consumption than a standard laboratory. Their miniaturization interferes with the multiple functions that the biochemical procedures require. In order to address this issue, our paper presents, for the first time, the integration on a single glass substrate of different thin film technologies in order to develop a multifunctional platform suitable for on-chip thermal treatments and on-chip detection of biomolecules. The proposed System on-Glass hosts thin metal films acting as heating sources; hydrogenated amorphous silicon diodes acting both as temperature sensors to monitor the temperature distribution and photosensors for the on-chip detection and a ground plane ensuring that the heater operation does not affect the photodiode currents. The sequence of the technological steps, the deposition temperatures of the thin films and the parameters of the photolithographic processes have been optimized in order to overcome all the issues of the technological integration. The device has been designed, fabricated and tested for the implementation of DNA amplification through the Polymerase Chain Reaction (PCR) with thermal cycling among three different temperatures on a single site. The glass has been connected to an electronic system that drives the heaters and controls the temperature and light sensors. It has been optically and thermally coupled with another glass hosting a microfluidic network made in polydimethylsiloxane that includes thermally actuated microvalves and a PCR process chamber. The successful DNA amplification has been verified off-chip by using a standard fluorometer.

Fabrication of integrated porous glass for microfluidic applications

This paper presents a method for the fabrication of integrated porous silica layers in microfluidic channel networks by microfabrication techniques. Porous silica is obtained by anodization of silicon, followed by full conversion of the porous silicon network into porous silica by means of thermal oxidation. A series of experiments were performed with various channel layouts to determine the critical parameters, including the I-V characteristics and the optimal working potential for stable pore formation, during anodic etching. Typical test structures were anodized in 5% HF for 15 min at 1 V, yielding an average pore size of around 5.4 nm and porosity of 49%. Complete conversion of porous silicon into porous glass was accomplished with wet oxidation at 900 °C. The average pore size and porosity of porous glass network were around 3.8 nm and 34%, respectively. This decrease in both pore size and porosity is caused by the increase in molar volume when silicon oxidizes to silicon oxide. The transparency and the hydrophilicity of porous glass layers are evidenced by means of monitoring the diffusion of Rhodamine B fluorescent dye through the porous network. This fabrication method can be applied to (3-D) structured microfluidic channels and it is envisioned that the resulting porous silica layers can be employed for a wide range of application areas, such as membrane technology, catalyst supports, chromatography and electrokinetics.