Insplorion has taken the general concept of LSPR-based sensing and made it applicable to a wide range of research areas through its novel technology Nanoplasmonic Sensing (NPS). The first section below contains a detailed description of the NPS sensor chip technology and functionality while in the second section the NPS measurement principle exploited in Insplorion’s research instruments is described.
NPS-chip Nanoarchitecture and Functionality
Nanoplasmonic Sensing in general exploits metallic nanoparticles, usually Ag or Au, as local sensing elements, which offer a combination of unique properties; including ultrahigh sensitivity, small sample amount/volume (due to the tininess of the “sensor”, i.e. a nanoparticle typically in the 50 – 100 nm size range) and capability for fast, real-time (millisecond time resolution) remote readout.
In Insplorion’s patent applied Nanoplasmonic Sensing (NPS) technology the sensing is realized through nanofabricated arrays of non-interacting, identical gold nanodisks on a transparent substrate. This gold nanodisk array (the “sensor”) is then covered with a thin (few tens of nm) film of a dielectric spacer layer (see figure to the right) onto which the studied sample material (e.g. nanoparticles or a thin film) is deposited. The sensor (nano)particles are thereby embedded in the sensor surface and not physically interacting with the studied nanomaterial, except via the LSPR dipole field. The latter penetrates though the spacer layer and has considerable strength also on and in proximity to its surface and can, therefore, sense dielectric changes there (see figure below).
The glass slide with the deposited Au sensor particles and the covering spacer layer can be regarded as a general sensor chip. In the unique nano-architecture of the Insplorion NPS sensor chip the spacer layer exerts the following functions:
- protection of the Au nanosensors from structural re-shaping;
- protection of the Au nanosensors from chemical interaction with the sample material;
- protection of the Au nanosensors from harsh/reactive environments;
- providing a tailored surface chemistry of the sensor chip, and thereby
- be either an inert substrate for the sample material, or
- participate actively in the studied process (e.g. spillover effects).
A major advantage of the NPS approach is that any material shape and size (e.g. very small nanoparticles down to 1 nm or films) and any material type (e.g. metal, insulator, polymer) can be studied on a wide range of substrate materials (i.e. spacer layers).
Link to Science article describing Nanoplasmonic Sensing more in detail (requires subscription, contact Insplorion for more information at firstname.lastname@example.org)
During an experiment in Insplorion’s instrument an optical extinction measurement is made through a quartz measurement cell/reactor in which the sensor chip is mounted (see figure below). The latter involves the detection of transmitted light, from a collimated white light source, through the sensor chip (via an optical fiber and the reactor walls) as a function of wavelength by an optical spectrometer (via a second optical fiber). Optical extinction spectra of the LSPR response, of the sensor chip, are detected with subsecond time resolution.
The optical response of the NPS sensor chips is characterized by a distinct peak at a certain wavelength in the extinction spectrum. The latter is caused by the strong interaction of the Au nanodisk sensors with light at the LSPR, through absorption and scattering. During an NPS experiment, the spectral position of the LSPR peak (i.e. the precise color of the sensor chip) is monitored as a function of time during a process that one wants to study/monitor e.g. where the sample material on the chip is interacting with molecules in the gas phase (see figure below) or is exposed to a temperature change. The color changes, which can be measured in real time (millisecond temporal resolution) and with 10-2 nm spectral resolution, can then be related, e.g., to the kinetics of a chemical process taking place in/on the sample material (e.g. a phase transition), changes in the surface coverage of a certain atomic/molecular species on the sample surface or the chemical energy dissipated by a chemical reaction running on a nanocatalyst.