Piezoresistive Membrane Surface Stress Sensors for Characterization of Breath Samples of Head and Neck Cancer Patients.

For many diseases, where a particular organ is affected, chemical by-products can be found in the patient's exhaled breath. Breath analysis is often done using gas chromatography and mass spectrometry, but interpretation of results is difficult and time-consuming. We performed characterization of patients' exhaled breath samples by an electronic nose technique based on an array of nanomechanical membrane sensors.

Double-side-coated nanomechanical membrane-type surface stress sensor (MSS) for one-chip-one-channel setup.

With their capability for real-time and label-free detection of targets ranging from gases to biological molecules, nanomechanical sensors are expected to contribute to various fields, such as medicine, security, and environmental science. For practical applications, one of the major issues of nanomechanical sensors is the difficulty of coating receptor layers on their surfaces to which target molecules adsorb or react. To have measurable deflection, a single-side coating is commonly applied to cantilever-type geometry, and it requires specific methods or protocols, such as inkjet spotting or gold-thiol chemistry.

Batch fabrication of gold-gold nanogaps by E-beam lithography and electrochemical deposition.

We report on the successful development of a well-controlled two-step batch nano-fabrication process to achieve nanometer-size gaps at the wafer scale. The technique is based on an optimized electron-beam lithography process, which enables the fabrication of nanogaps in the range (15 ± 4) nm. Following this first step, the feedback-controlled electrochemical deposition of gold from an aqueous HAuCl4-based electrolyte is applied to further reduce the size of the gap down to about 0.

Two dimensional array of piezoresistive nanomechanical Membrane-type Surface Stress Sensor (MSS) with improved sensitivity.

We present a new generation of piezoresistive nanomechanical Membrane-type Surface stress Sensor (MSS) chips, which consist of a two dimensional array of MSS on a single chip. The implementation of several optimization techniques in the design and microfabrication improved the piezoresistive sensitivity by 3~4 times compared to the first generation MSS chip, resulting in a sensitivity about ~100 times better than a standard cantilever-type sensor and a few times better than optical read-out methods in terms of experimental signal-to-noise ratio. Since the integrated piezoresistive read-out of the MSS can meet practical requirements, such as compactness and not requiring bulky and expensive peripheral devices, the MSS is a promising transducer for nanomechanical sensing in the rapidly growing application fields in medicine, biology, security, and the environment.

Nanomechanical membrane-type surface stress sensor.

Nanomechanical cantilever sensors have been emerging as a key device for real-time and label-free detection of various analytes ranging from gaseous to biological molecules. The major sensing principle is based on the analyte-induced surface stress, which makes a cantilever bend. In this letter, we present a membrane-type surface stress sensor (MSS), which is based on the piezoresistive read-out integrated in the sensor chip.

Implementation and characterization of a quartz tuning fork based probe consisted of discrete resonators for dynamic mode atomic force microscopy.

The quartz tuning fork based probe {e.g., Akiyama et al.

Sub-ppm detection of vapors using piezoresistive microcantilever array sensors.

The performance of microfabricated piezoresistive cantilever array sensors has been evaluated using various vapors of volatile organic compounds including alkanes with different chain length from 5 (n-pentane) to 14 (n-tetradecane). We demonstrate that piezoresistive microcantilever array sensors have the selectivity of discriminating individual alkanes in a homologous series as well as common volatile organic compounds according to principal component analysis. We developed a new method to evaluate the sensitivity, taking advantage of the low vapor pressures of alkanes with longer chains, such as n-dodecane, n-tridecane and n-tetradecane, under saturated vapor conditions.

The measurement of biomechanical properties of porcine articular cartilage using atomic force microscopy.

We have recently demonstrated that indentation-type atomic force microscopy (IT-AFM) is capable of detecting early onset osteoarthritis (OA) (Stolz, 2009). This study was based on biopsies, using a desk-top commercial atomic force microscope (AFM). However, cartilage analysis in the knee joints needs to be non-destructive to avoid new seeding points for OA by the taking of biopsies.

Conductive supports for combined AFM-SECM on biological membranes.

Four different conductive supports are analysed regarding their suitability for combined atomic force and scanning electrochemical microscopy (AFM-SECM) on biological membranes. Highly oriented pyrolytic graphite (HOPG), MoS(2), template stripped gold, and template stripped platinum are compared as supports for high resolution imaging of reconstituted membrane proteins or native membranes, and as electrodes for transferring electrons from or to a redox molecule. We demonstrate that high resolution topographs of the bacterial outer membrane protein F can be recorded by contact mode AFM on all four supports.

Characterization of microfabricated probes for combined atomic force and high-resolution scanning electrochemical microscopy.

A combined atomic force and scanning electrochemical microscope probe is presented. The probe is electrically insulated except at the very apex of the tip, which has a radius of curvature in the range of 10-15 nm. Steady-state cyclic voltammetry measurements for the reduction of Ru(NH3)6Cl3 and feedback experiments showed a distinct and reproducible response of the electrode.