On-chip optical detection of chemiluminescent reactions is presented. The device is based on the integration of thin film hydrogenated amorphous silicon photosensors on a functionalized glass substrate ensuring both a good optical coupling and an optimal separation between biological or chemical reagents and the sensing elements. The sensor has been characterized and optimized using the chemiluminescent system composed by the enzyme horseradish peroxidase (HRP) and luminol/peroxide/enhancer cocktail. The detectability of HRP is at the attomole level with a sensitivity of 1.46 fA/fg. Experiments, involving the detection of immobilized bio-specific probes on the functionalized surface have been performed both in bulk and microfluidics regime, proving the ability of the system to effectively detect chemiluminescent reactions and their kinetics. In particular, results achieved using conventional polydimethylsiloxane microfluidics for samples and reagents handling confirmed the good detection capabilities of the proposed system.

In this paper, we present the preliminary results of an ELISA-on-chip device, intended as a technological demonstrator of a novel analytical system suitable for the diagnosis and follow-up of celiac disease. The idea of the work is to combine an array of amorphous silicon photosensors with a pattern of a poly(2-hydroxyethyl methacrylate) polymer brush film, which acts as anchor for the immobilization of gliadin peptides containing the celiac disease epitopes. Recognition relies on a sandwich immunoassay between antibodies against the peptides and secondary antibodies marked with horseradish peroxidase to obtain a chemiluminescent signal. Detection is based on the measurement of photocurrent induced in the array of amorphous silicon photosensors by the chemiluminescent signal. An ad-hoc procedure has been developed in order to enable the fabrication of the photodiode array and the polymer brush pattern on the two sides of the same glass substrate ensuring the compatibility of the different technological steps. The sensitivity and the selectivity of the chip for multiplex immunoassays were demonstrated using two gliadin peptides (VEA and DEC). In particular, we found that the average amount of the bound HRP revealed by our analytical protocol is 3.5(±0.3) × 10⁻⁶ pg μm⁻² and 0.85(±0.3) × 10⁻⁶ pg μm⁻² for specific and non-specific interactions, respectively.

In this paper, we propose the use of an array of amorphous silicon (a-Si:H) p-i-n diodes to monitor the spatial temperature distribution over a thin film heater used for thermal treatments in lab-on-chip systems. The effects of heater geometry and operating conditions on the spatial temperature distribution have been preliminarily investigated by using COMSOL Multiphysics, coupling the electrostatic problem with the thermal problem via the Joule effect. Depending on the analyzed system, nonuniform temperature profiles can be induced over the heater surface revealing the need for a temperature point-monitoring. An example of whole device, constituted by a serpentine shaped TiW/Al/TiW thin film heater and five a-Si:H diodes deposited between the resistor meanders, has been fabricated on a microscope glass slide and characterized. Voltage-temperature characteristics of the a-Si:H sensors, measured at constant forward current, show a sensitivity around 2.8mV/°C. The spatial temperature distribution along the heater has been derived measuring the voltage across each a-Si:H diode. A good agreement between modeled and measured data is obtained, demonstrating the suitability of the a-Si:H array as temperature distribution sensors in lab-on-chip application. © 2011 IEEE

The presence of ochratoxin A (OTA) in different food commodities deserves great attention because of its toxic and carcinogenic effects on humans and animals. In this paper, we report on the detection of OTA both in standard solutions and in contaminated samples of red wine by using amorphous silicon photosensors. The method relies on the excitation by ultraviolet radiation of the toxin molecules and on the absorption of the toxin reemitted light by the photosensor. The device is a p-i-n stacked structure, whose electro-optical characteristics have been optimized in order to maximize the photosensor responsivity and the limit of detection. For standard solutions, we found minimum detected OTA amount to be equal to 0.1 ng, while for contaminated red wine samples the technique coupled with very simplified and rapid extraction procedures has allowed the detection of OTA at the 1-ppb level.