In his visionary 1959 lecture at Caltech, Feynman envisaged the potential of the ability to manipulate matter at the atomic scale. I discuss implementations of Feynman's vision in the field of nanosensors and perspectives of its further development and applications.

Since its origin in the early 1980s, the noise-injection based stochastic resonance technique has spearheaded a novel counter-intuitive approach toward improving sensor performance. Within this approach, named Active Signal Processing, instead of removing system noise by filtering (Passive Signal Processing), it is possible to improve signal-to-noise ratio (SNR) by injecting noise into the measurement. ViaLogy LLC. has pioneered the development and demonstration of Quantum Resonance Interferometry (QRI), a quantum stochastic resonance (QSR)-based technique for improving SNR. The core of QRI processing involves the QSR-based generation of a Quantum Expressor Function (QEF), which characterizes the system of interest by encoding within it the noise environment, minimum level of detection, and the precision of measurement. Using digital post-processing of sensor information, QRI can determine the presence of a signal by the destruction of the resonance condition responsible for generating the system QEF. For applications aimed at detecting the presence of a weak signal, the strength of the signal is proportional to the number of iterations of the algorithm required for destruction of the resonance; the fewer the iterations, the stronger the signal. The application of QRI for detecting the presence of weakly expressing genes in fluorescent DNA microarrays will be described.

In this study, HeLa cells were transfected to express a recombinant transmembrane domain of the platelet-derived growth factor receptor. Silver nanoparticle (Ag-NP) functionalized with terminal hydrazide was employed to specifically target the ketone-conjugated cell surface proteins. In addition, a nitrile functional group was incorporated onto the Ag nanoprobe to provide unique vibrational signature (∼ 2230 cm−1) in a window which is free from other cellular components. The designed Ag nanoprobe functions as both recognition and transduction elements in the detection of the expressed cell surface protein. Scanning electron microscopy and surface enhanced Raman spectroscopy (SERS) imaging of the nanoparticle (NP) labeled HeLa cells revealed that all the observed intense SERS signals originated from aggregated NPs. Although isolated Ag-NPs is capable of SERS enhancement, its enhancement factor is beyond the detestability of such imaging experiments. The results have implication in the future design of SERS nanosensors for in vivo detection application.

Recently, lattice-matched Zn0.46Cd0.54Se/ZnCdMgSe multiple-quantum-wells (MQWs) have been recognized as very promising materials to fabricate intersubband (ISB) devices such as quantum cascade lasers and mid-infrared photoconductors. These structures have important applications in biological and chemical detections. The ISB transition covers a wide mid-infrared wavelength range from 1.3 μm to a few tens of μm.

In this work, two heavily doped n-Zn0.46Cd0.54Se/Zn0.24Cd0.25Mg0.51Se MQW structures have been grown on InP (001) substrate by molecular beam epitaxy. Temperature dependent steady-state photoluminescence (SSPL), temperature dependent time- resolved photoluminescence (TRPL), and Fourier transform infrared spectroscopy (FTIR) were performed to characterize their interband and ISB properties. These two MQW samples have similar structures except different well widths and different number of periods. The integrated SSPL intensities and the PL decay times of the MQWs were measured as functions of temperature in the range from 77 K to 290 K. The luminescence efficiency of the sample with 28 Å well width is larger than that of the sample with 42 Å well width although both samples exhibit similar temperature dependence of PL intensity. Time-resolved PL measurements show that the PL decay times of both samples decrease with increasing temperature. From 77 K to 290 K, the decay time of the sample with 28 Å well width is in the range of 440 ps ∼ 120 ps and is much longer than that of the sample with 42 Å well width, which is in the range of 65 ps ∼ 25 ps. Strong non-radiative recombinations dominate the luminescence behavior of the wider MQWs. Intersubband absorption spectra of the samples were measured by FTIR and show peak absorption at wavelengths of 3.99 μm and 5.35 μm for the MQWs with well widths of 28 Å and 42 Å, respectively, falling within the 3-5 Åm range, which is of great interest for the infrared photodetector applications.

We examined lanthanum doped lead barium titanate films for temperature measurements of photonic crystal - MEMS devices. Films were deposited by sol-gel techniques and crystallized in air above 650°C. X-ray diffraction spectra consistent with the perovskite structure were detected. The room temperature dielectric constant was ∼570 at 10 kHz of La-doped (0.3 mol%) Pb0.3Ba0.7TiO3 films. These films had a remanent polarization of ∼20μC/cm2 and a coercive field of 145 kV/cm. The leakage current density was ∼ 2×10−7 amps/cm2 at 100 kV/cm field. The resistivity of the films extracted from the linear region of the I-V data (electric fields in excess of 100 kV/cm) measured as a function of temperature shows an increase in resistivity at temperatures above Tc (120°C for BaTiO3 and 240°C for Pb0.3Ba0.7TiO3) of the film consistent with positive coefficient of resistance (PTCR) effect. However, the change in resistance was small when compared to bulk samples of similar compositions.

A sub-50 nm biomolecular direct electrical-detection structure integrated with micro- and nano-fluidic systems has been constructed. These devices are composed of integrated microfluidic channels in PDMS and nanofluidic channels in silicon oxide. These in turn are all integrated with a nano-gap sensing structure which has metallic electrodes. The microfluidic channel in PDMS provides access to the nanofluidic channel feeding the nano-gap sensing structure. We provide a demonstration of the bio-molecular sensing capabilities of our device by using the carboxyl-amino group interaction and a nano-gap structure with gold electrodes. First, probe molecules with amino groups are infused through the fluidic system to the nano-gap and are self-assembled onto the gold electrodes via thiolate bonding. Then target molecules with terminating carboxyl groups are infused to bind with the probe molecules. Impedance changes are measured electrically at each infusing and binding step using an Agilent 4284A impedance analyzer thereby detecting the appearance of each molecule type as it passes through the system. We are able to detect about 15% impedance changes with the carboxyl-amino binding occurrence.

Nano-gap metal oxide semiconductor (MOS) capacitors were studied to evaluate their limitations in applications of dielectric spectroscopy in living cells. The purpose was to optimize the design of a transducer to avoid interfacial polarization at the electrodes. Silicon IC technology was selected for designing processes in which we could limit electric double layer impedance by precisely controlling dielectric thickness of the capacitors in the range of 17 to 150 nm. The working capacitance was defined by lateral oxide etching of capacitor structures of various configuration to ensure high perimeter to area ratio. Highly doped n+ polysilicon and n+ implanted Si substrate were acting as capacitor's electrodes. Restrictions known from CMOS circuits regarding oxide leakage current, which depends on geometry and increases with the gate area were taken into account. To allow for testing cells (yeasts), which have larger dimensions than nano structures it was necessary to include cell manipulation using dielectrophoresis (DEP). Entrapment of cells at the electrode perimeter preceded electrical measurements. Our focus in analyses was on the frequency dependence of impedance parameters.

We have simulated metallo-dielectric photonic crystals that are sharp thermal emitters at infrared wavelengths, and are being employed in gas sensors. The simulations were performed with a rigorous scattering matrix approach where Maxwell's equations are solved in Fourier space. These metallo-dielectric photonic crystals consist of a sub-wavelength hole array in a metal layer coupled to a two-dimensional photonic crystal of the same periodicity. The sub-wavelength hole array has an enhanced transmission mode that couples to a guided mode of the photonic crystal. The transmissive mode of the hole array is absorbed by the photonic crystal to create a sharp absorption and reflective minimum feature found for a range of lattice spacing. The structure thermally emits in a narrow band of wavelengths controlled by the lattice spacing that can be tuned over the infrared region. The underlying physics of this emissive device is modeled with rigorous scattering matrix simulations.

A novel photo sensor pixel using a one-dimensional (1D) photonic crystal structure incorporating photoconductive layers has been realized. The fabricated device exploits mode discrimination to provide simultaneous multispectral photo sensing capability. Resonant cavity enhancement (RCE) design allows the use of very thin photoconductive layer to achieve dramatically suppressed shot noise, as well as high quantum efficiency. Low cost amorphous silicon is used to be photoconductive material and the simply fabrication process is completely CMOS-compatible. Detectivities as high as 2.6×1010 cmHz1/2W−1 and 2.0×1010 cmHz1/2W−1 at the two pre-selected wavelengths, 632nm and 728nm, were achieved, respectively.

This paper reports the integration of poled 10μm +/- 1μm P(VDF-TrFe) copolymer thin films with an adapted non-volatile, foundry-compatible CMOS structure (CνMOS) for the potential purposes of in-vivo piezoelectric and pyroelectric sensing. This structure allows for direct, reliable interaction between the sensing transducer and the highly sensitive MOSET gate stack without the need for an external reference electrode or chopper, as other designs may require.

The coupling of semiconductor field-effect devices (FED) together with chemical and biological recognition elements, like functional intelligent materials, biomolecules and living cells, represents an attractive platform for the creation of different (bio-)chemical sensors, multi-parameter analysis systems and bio-chips. This paper summarises recent developments and current research activities in the field of (bio-)chemically modified FEDs, scaling down from capacitive EIS (electrolyte-insulator-semiconductor) sensors and LAPS (light-addressable potentiometric sensor) to ISFETs (ion-sensitive field-effect transistor) that have been realised in our laboratory. Selected examples of application of ISFETs for the detection of physical parameters in liquids are presented, too. With the aim of future development of nano-devices for the detection of single biomolecules, the possibility of a simple preparation of different self-aligned nano-structures by using conventional photolithography and pattern-size reduction technique has been experimentally demonstrated.

Uncooled double-cantilever microbolometers have the potential of reaching a noise-equivalent temperature difference (NETD) approaching the theoretical limit and thus have gained increasing interest. Each pixel of the device consists of two overlapping bimaterial cantilevers that deflect in opposite directions as their temperature rises due to the absorption of incident infrared radiation. This paper reports recent progress in the development of these double-cantilever focal plane arrays (FPAs), including fabrication and post-process curvature modification.

A miniaturized, fully-automated, PCR-based detection system has been developed for the rapid detection of the pathogenic bacterium Bacillus anthracis. Monolithic silicon DNA purification / real-time PCR chips were fabricated and tested for their ability to purify and detect DNA from bacterial cells. Using silica-coated microstructures and chemical-based lysis, nucleic acids could be isolated, washed and eluted for subsequent real-time PCR. These microstructures were integrated into a detection microchip containing two distinct regions, one for DNA purification and one for real-time PCR. Using an automated detection platform with integrated microprocessor, pumps, valves, thermocycler and fluorescence detector, target bacterial DNA was detected by real-time PCR amplification using SYBR Green fluorescent dye. As few as 40 B. anthracis cells could be detected using this system with an average time for detection of 60 min. Detection was augmented by on-chip melting curve analysis capable of differentiating between positive and false-positive results.

A new technique for nanoparticle sizing that allows visualisation of nanoscale particles in liquids on an individual basis is described. The technology comprises a metallised optical element illuminated by laser beam at the surface of which nanoscale particles in suspension can be directly visualised, sized and counted in real time using only a conventional optical microscope fitted with a low cost camera and a dedicated analytical software package.

Herein, we describe a biomimetic approach aimed at the development of synthetic biohybrid materials inspired by nature's sensing and actuating mechanism of action. The biomaterials are based on the incorporation of the hinge-motion binding protein calmodulin (CaM) and its low affinity ligand phenothiazine (TAPP) within the bulk of an acrylamide hydrogel network, which is accomplished through covalent binding. At the initial state and in the presence of Ca2+ ions, CaM interacts with TAPP creating chemical (non-covalent) cross-links within the bulk of the hydrogel, forcing the material to assume a constrictive configuration. Upon the removal of Ca2+, CaM releases TAPP, breaking the non-covalent cross-links within the bulk of the hydrogel and letting the material relax into a swollen state. The same type of effect is observed when a higher affinity ligand for CaM, like chlorpromazine (CPZ), is employed. In the presence of CPZ, the protein releases TAPP and binds CPZ, allowing the biomaterial to swell into a relaxed state. This swelling response of the biomaterial is reversible, and is directly related to the levels of CPZ used. The sensing and subsequent actuating mechanism of the CaM-based stimuli-sensitive hydrogels makes them suitable for a variety of applications, including sensing, mechanical actuation, high-throughput screening, and drug delivery. Additionally, it is shown that the CaM-based stimuli-sensitive hydrogels developed present unique mechanical properties, suitable for integration within microfluidics and MEMS structures. It is envisioned that these biomaterials will find a number of applications in a variety of fields, including drug delivery.