ICInnovation

Nanotechnology is very enabling for the development of a new range of ultrasensitive sensors. Thanks to miniaturization down to micron & nano level the following features can be realized:

• function integration: sensing, data processing and storage, wireless communication all integrated in one chip
• multi parallel analysis for high throughput
• matrix arrays for better sensitivity and directional information
• high sensitivity towards single cell/molecule detection and zeptogram (10^-21 gram) sensitivity
• efficient thermal and material transport, less chemical waste, low power consumption
• energy scavenging (solar, temperature, mechanical) for continuous power supply
• portable, wearable, self operating at remote point of analysis
• enabling mass production, low cost, disposable

Mechanical sensors

Mechanical nanosensors are based on the displacement of a tiny cantilever, beam or nanowire under the influence of an inertial force, vibration or pressure difference. The displacement is being measured via a change in the system capacitance or electronically (field effect transistor), optically (laser deflection) or via a piezo surface charge effect (ZnO). Thanks to the nanometer dimensions, very small forces can be detected down to a range of 10^-18 N. Current world record even a sensitivity of 10^-19 gram, or 100 zepto(10^-21) grams. Examples are 3D-acceleration sensors, pressure sensors and vibration sensors.

Radiation sensors

EM radiation can be sensed using a nano-sized dipole antenna with optical dimensions (50 nm – 100 μm length) connected to a micro bolometer matrix array. More accurate is the use of a quantum well structure: here electrons tunnel through a barrier under the activation of external radiation. This enfavours a high signal to noise ratio and a large number of quantum wells on a chip yields a large signal output. Main applications f are infrared and THz radiation.

Chemical sensors

For chemical sensing many different techniques are available and also still in development. Nanotechnology techniques are usually applied in combination wit a lab-on-chip microsystem for the fluidic processing, filtering, and pretreatment. A short overview:

Fluidic

• fluorescence: lab-on-chip specific binding with a fluorescent quantum dot (10^-12/13 mol/liter)
• magnetic: specific binding with a magnetic particle with GMR readout (10^-13/14 mol/liter)
• optical: specific binding at a nanostructured surface, readout by surface plasmon resonance (10^-8/9 mol/liter)
• planar waveguide fluorescence (10^-13 mol/liter)
• electrochemical: chemical reaction with a metal oxide nanostructure on chip (10^-9 mol/liter) or in combination
• with enzymatic assisted charge transfer (10^-15/16 mol/liter)

Gaseous

• chemical: electron transfer with a metal oxide nanostructure on chip, nanotubes/wires (10^-9, ppb-parts per billion)
• optical: specific binding of airborn particles to a nanostructured surface, read-out by surface enhances raman spectroscopy (10^-12, ppt-parts per trillion)
• mechanical: specific binding to a resonating cantilever (10^-12) or nanowire (10^-15)

Magnetic sensors

GMR, giant magnetic resistance and TMR, tunneling magnetic resistance, are magnetic sensor/readers using the quantum effects of electrons (spintronics) flowing in a confined space of a nanolayer under the influence of magnetic field. A sensitivity of 10^-9 Tesla can be achieved. Recently IBM has developed of a magnetic resonance force microscope (MRFM, a magnetic tip on a ultrasentive cantilever) to detect and analyse the spin of electrons in a sample.

Miniature X-ray sensors

Carbon nanotubes are very effective electron emitters, originally being developed for flat electron displays. As a spinoff carbon nanotubes are now being applied as a miniature electron source to generate for X-rays. X-ray sources down to millimeter scale are now in development, to be used in handheld X-ray detection devices.

Surface enhanced raman spectroscopy

Surface-Enhanced Raman spectroscopy (SERS) on chip can provide ultra low trace level chemical detection of airborne explosives and contraband molecules with a sensitivity in the parts-per-trillion range. It allows the remote detection of these materials at room temperature. Examples of detection at ppt level are: TNT (dynamite), DNT, RDX (plastic), TATP (liquid), PETN (high), picric acid ('home-made' explosive), DMDNB (taggant for plastic explosives) and traces of cocaine.