Detecting and identifying molecular signatures in air and liquid have broad applications in markets ranging from industrial to consumer applications. Today, such capability is limited to either expensive large lab instruments or narrowly capable products (ex: a home CO detector).  iSense has developed and extensively tested a high dimensional colorimetric sensor array (CSA) that is low cost, compact, disposable, robust and easy to use. We have manufactured more than 100,000 CSAs proving the repeatability and precision of the sensor results. A strong and robust patent portfolio of the sensor and it’s applications is in place.

The CSA technology employs a disposable array of chromogenic indicators that constitute a signal similar to a mammalian olfaction system, in that there is not a single receptor for every unique odor, but instead each gas is detected as a sum of responses across multiple partially-promiscuous receptors.  While colorimetric sensing is an old technology and conceptually simple to eye, the CSA technology, which incorporates many indicators into an array, is both elegant and scientifically powerful.  An array of indicators (typ. 16≤n≤120) is printed on a small (≈1 in2) piece of paper-like membrane.  This printed array is then exposed to given analytes, at which point a subset of the indicator spots will respond by changing color.  The main advantage of CSAs compared to other array based sensor technologies lies in the simplicity of their design and data acquisition.  A wide range of chemicals have been examined using these chromogenic indicators, and we have demonstrated (1) qualitative identification of chemicals in both liquid and vapor phases; (2) quantification of analyte concentrations; and (3) differentiation of complex mixtures.  Additionally, the sensor can be customized to determine concentrations of a single target VOC in complex mixtures.

Sensor Background and Capabilities.

The CSA system has two major components: a disposable sensor and an imaging device to measure color changes.  The detection event is observed as numerous printed dots characteristically change color upon exposure.  These events can be recorded with a typical imaging device.  While kinetic information may be obtained by repeatedly scanning the CSA, typically ‘before’ and ‘after’ images are sufficient for detection and identification.  Given two (before and after exposure) sensor images, a color difference map can be generated by superimposing and subtracting the two images.  This color difference map can be quantified as a high dimensional vector of RGB values.  These vectors can be used to discriminate between different analytes while retaining useful information about resemblances between chemically similar species.  This is both unique among molecular sensor technologies and highly significant for forensic applications:  even in cases where the color change pattern of an unknown analyte is not in the library, we will be able to tell what an analyte most closely resembles in its chemical properties.

Toxic Industrial Chemicals.
As a demonstration of our classification power, we have previously reported the detection of 20 different toxic industrial chemicals (TICs).  Clear differentiation among 20 different TICs was been easily achieved within minutes of exposure as shown below.  The difference maps highlight the sensor’s ability to discriminate among all chemical classes shown, even closely related compounds, such as ammonia and methylamine.

Complex mixtures

In addition to the toxic industrial chemicals, the CSA has proven particularly well suited for distinguishing the high-dimensional volatile mixtures.  Coffee provides a readily available example of discrimination among closely similar complex mixtures. Using an unsupervised cluster analysis method (e.g., HCA), 10 commercial coffees and controls were correctly differentiated without any error. The method underlying this successful identification of complex mixtures rely on treating the mixture as a single analyte. Compared with traditional techniques using complicated separation techniques such as GC-MS, this approach is less expensive and easier to operate. While mixtures in the field are difficult to predict, diversifying our pesticide library with different background gases will be part of our path to success.

In summary the CSA is a printed, inexpensive, disposable sensor that is:

Highly sensitive: low ppb (parts per billion) detection limit.

Highly selective: VOCs (volatile organics), TICs (toxics), bio-signatures…

High dimensional: discrimination of complex mixtures.

On-site analysis: real time results with a smart phone or IoT device.

Flexible: liquid & air analysis.

Proven>100,000 sensors have been produced and tested with consistent high performance; supported by more than 60 peer-reviewed publications.

IP Protected: Strong issued and pending patents.