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This paper describes the optimal implementation of three newly conceived sensors for both health and environmental applications, utilizing a wide range of detection methods and complex nanocomposites. The first one is inorganic and based on matrices of calcium oxide, the second is based on protein arrays and a third one is based on Langmuir-Blodgett laccase multi-layers. Special attention was paid to detecting substances significant to the environment (such as carbon dioxide) and medicine (drug administration, cancer diagnosis and prognosis) by means of amperometric, quartz crystal microbalance with frequency (QCM_F) and quartz crystal microbalance with dissipation monitoring (QCM_D) technologies. The resulting three implemented nanosensors are described here along with proofs of principle and their corresponding applications.

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Measurement of the ac photocurrent in metal/insulator/semiconductor capacitors can be used as a tool to measure minority-carrier diffusion and lifetime. The amplitude of the ac photocurrent generated at a silicon surface biased into inversion depends on the number of excess minority carriers present at that surface. By comparing this amplitude when intensity-modulated light is directed to each side of the same device, minority-carrier diffusion from the back to the front of the device can be characterized. An analytical model of this transport process predicts the dependence of the ac photocurrent on frequency and wafer thickness, and allows the determination of a value of the bulk lifetime free of the influence of surface recombination. Measurements under low-light intensity levels are presented on n-type silicon wafers with lifetimes in the 10–100 μs range. Lifetimes are found about a factor of 2 lower than those measured with noncontact photoconductive decay, at high-light intensity levels. This is expected due to the difference between high- and low-level minority-carrier injection. Fitting the data to the model also yields a value of 115 μm for the average depth at which carriers are generated and diffuse to the front with backside illumination at 940 nm.

The present work describes a simple chamber suitable for morphological investigations by implementing the atomic force microscopy (AFM) in controlled experiments. The novelty of our application stems from proposing an open system located in between the expensive, ultra-high-vacuum instruments and those working in air conditions, both available on the market. The former are in fact designed to obtain a detailed inspection of the samples and to develop particular geometries on them, by means of nanolithography or nanomanipulation, while the latter are designed for and used in all the situations in which the environmental conditions do not cause artifacts, problems, or formation of spurious particles on the samples during imaging. We have developed an ad hoc system based on a high-vacuum chamber (up to 10−6 Torr), which allows us to work under controlled-atmosphere conditions. The system, therefore, can be used with most of the samples which suffer from higher pressures, and exploits all the benefits arising from a controlled environment. We have equipped the chamber with an AFM and a sample-holder/mover. An external X–Y–Z motion controller, completely automated, allows the easy positioning of the sample under the sensing cantilever and the consequent relative approach. Experiments with the proposed system are presented, in which the control of environmental conditions during AFM measurements has been investigated with satisfactory results.

A customized atomic force microscopy (AFM) instrument optimized for imaging protein crystals in solution is described. The device was tested on crystals and Langmuir-Blodgett (LB) films of two proteins with quite different molecular weights. This approach enables the periodicity and morphology of crystals to be studied in their mother liquid, thereby preserving the native periodic protein crystal structure, which is typically destroyed by drying. Moreover, the instrument appears to distinguish protein crystals from salt crystals, which under the optical microscope are frequently quite similar, the difference between them often being revealed only during x-ray analysis. AFM estimates of the packing, order, and morphology of the given single proteins appear quite similar in the LB thin film and in the crystals, which means that routine crystal measurements can be performed at high resolution. The AFM consists of a custom-built measuring head and a homemade flexible SPM controller which can drive the head for contact, noncontact and spectroscopy modes, thus providing the user with a high degree of customization for crystal measurement.

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Highly oriented bacteriorhodopsin films were deposited using a specially designed procedure of electric field assisted monolayer formation. The self-assembly of the monolayer at the air/water interface was monitored by the increase of the surface pressure. The monolayers were transferred onto solid substrates by the Langmuir-Schaefer technique. Electrical measurements on the films with a specially designed chamber confirmed the improved orientation of the films. Possible application of the films in practical devices such as a transducer for biosensor is discussed, keeping in mind features and inherent limitations when compared with existing silicon transducers.