Marc K. von Gunten

Miniature Near-Infrared (NIR) Spectrometer Engine For Handheld Applications

While substantial progress has been made recently towards the miniaturization of Raman, mid-infrared (IR), and near-infrared (NIR) spectrometers, there remains continued interest from end-users and product developers in pushing the technology envelope toward even smaller and lower cost analyzers. The potential of these instruments to revolutionize on-site and on-line applications can only be realized if the reduction in size does not compromise performance of the spectrometer beyond the practical need of a given application. In this paper, the working principle of a novel, extremely miniaturized NIR spectrometer will be presented. The ultra-compact spectrometer relies on thin-film linear variable filter (LVF) technology for the light dispersing element. We will also report on an environmental study whereby the contamination of soil by oil is determined quantitatively in the range of 0-12% by weight of oil contamination. The achieved analytical results will be discussed in terms of the instruments competitiveness and suitability for on-site and in-the-field measurements.

Pharmaceutical Raw Material Identification Using Miniature Near-Infrared (MicroNIR) Spectroscopy and Supervised Pattern Recognition Using Support Vector Machine

Near-infrared spectroscopy as a rapid and non-destructive analytical technique offers great advantages for pharmaceutical raw material identification (RMID) to fulfill the quality and safety requirements in pharmaceutical industry. In this study, we demonstrated the use of portable miniature near-infrared (MicroNIR) spectrometers for NIR-based pharmaceutical RMID and solved two challenges in this area, model transferability and large-scale classification, with the aid of support vector machine (SVM) modeling. We used a set of 19 pharmaceutical compounds including various active pharmaceutical ingredients (APIs) and excipients and six MicroNIR spectrometers to test model transferability. For the test of large-scale classification, we used another set of 253 pharmaceutical compounds comprised of both chemically and physically different APIs and excipients. We compared SVM with conventional chemometric modeling techniques, including soft independent modeling of class analogy, partial least squares discriminant analysis, linear discriminant analysis, and quadratic discriminant analysis. Support vector machine modeling using a linear kernel, especially when combined with a hierarchical scheme, exhibited excellent performance in both model transferability and large-scale classification. Hence, ultra-compact, portable and robust MicroNIR spectrometers coupled with SVM modeling can make on-site and in situ pharmaceutical RMID for large-volume applications highly achievable.

Pocket-Size Near-Infrared Spectrometer for Narcotic Materials Identification

While significant progress has been made towards the miniaturization of Raman, mid-infrared (IR), and near-infrared (NIR) spectrometers for homeland security and law enforcement applications, there remains continued interest in pushing the technology envelope for smaller, lower cost, and easier to use analyzers. In this paper, we report on the use of the MicroNIR Spectrometer, an ultra-compact, handheld near infrared (NIR) spectrometer, the, that weighs less than 60 grams and measures < 50mm in diameter for the classification of 140 different substances most of which are controlled substances (such as cocaine, heroin, oxycodone, diazepam), as well as synthetic cathinones (also known as bath salts), and synthetic cannabinoids. A library of the materials was created from a master MicroNIR spectrometer. A set of 25 unknown samples were then identified with three other MicroNIRs showing: 1) the ability to correctly identify the unknown with a very low rate of misidentification, and 2) the ability to use the same library with multiple instruments. In addition, we have shown that through the use of innovative chemometric algorithms, we were able to identify the individual compounds that make up an unknown mixture based on the spectral library of the individual compounds only. The small size of the spectrometer is enabled through the use of high-performance linear variable filter (LVF) technology.

Miniature near-infrared spectrometer for point-of-use chemical analysis

Point-of-use chemical analysis holds tremendous promise for a number of industries, including agriculture, recycling, pharmaceuticals and homeland security. Near infrared (NIR) spectroscopy is an excellent candidate for these applications, with minimal sample preparation for real-time decision-making. We will detail the development of a golf ball-sized NIR spectrometer developed specifically for this purpose. The instrument is based upon a thin-film dispersive element that is very stable over time and temperature, with less than 2 nm change expected over the operating temperature range and lifetime of the instrument. This filter is coupled with an uncooled InGaAs detector array in a small, rugged, environmentally stable optical bench ideally suited to unpredictable environments. The resulting instrument weighs less than 60 grams, includes onboard illumination and collection optics for diffuse reflectance applications in the 900-1700 nm wavelength range, and is USB-powered. It can be driven in the field by a laptop, tablet or even a smartphone. The software design includes the potential for both on-board and cloud-based storage, analysis and decision-making. The key attributes of the instrument and the underlying design tradeoffs will be discussed, focusing on miniaturization, ruggedization, power consumption and cost. The optical performance of the instrument, as well as its fit-for purpose will be detailed. Finally, we will show that our manufacturing process has enabled us to build instruments with excellent unit-to-unit reproducibility. We will show that this is a key enabler for instrumentindependent chemical analysis models, a requirement for mass point-of-use deployment.

Advances in miniaturized spectral sensors

Recent advances in the deposition of patterned thin film spectral filters have enabled a new class of radically miniaturized spectral sensors. This new technology enables numerically large arrays of spectral bandpass filters with unprecedented manufacturing economy. For example, a 64-channel array occupying two square millimeters and spanning 400-900 nm can be deposited with as few as eight coating steps. Mating this filter array to a photodiode array yields a tiny multispectral sensor with diverse applications. The bandpass filters are single-cavity Fabry-Perot designs with common top and bottom mirrors. The dielectric spacer layer between them determines the passband wavelength and is patterned to differing thicknesses using a binary scheme, i.e., each successive “sub-spacer” layer is half the thickness of the previous one. The technical challenge is uniformly patterning and depositing thinner and thinner sub-spacers, which can be only a few nanometers thick. We have demonstrated 64-channel arrays covering the spectral range of 400-900 nm and 775-1075 nm. These arrays have been mated to high-responsivity 2D silicon detectors, in much the same way that linear variable filters are mated to linear detector arrays. The resulting sensor is less than 3 x 3 x 1 mm in size and ideal for integration into mobile devices, wearable electronics, autonomous aerial vehicles, and countless industrial applications. Sensor performance is currently being evaluated for food quality and freshness measurement, drug identification, fuel quality measurement, explosives detection, colorimetry and illumination measurement, solar flux monitoring, remote sensing, and myriad other applications.

Solid-state 488-nm laser based on external-cavity frequency doubling of a multi-longitudinal mode semiconductor laser

Results for a new compact 488 nm solid-state laser for biomedical applications are presented. The architecture is based on a multi-longitudinal mode external cavity semiconductor laser with frequency doubling in a ridge waveguide fabricated in periodically poled MgO:LiNbO3. The diode and the waveguide packaging have been leveraged from telecom packaging technologies. This design enables built-in control electronics, low power consumption (≤ 2.5 W) and a footprint as small as 12.5 x 7 cm. Due to its fiber-based architecture, the laser has excellent beam quality, M2 <1.1. The laser is designed to enable two light delivery options: free-space and true fiber delivered output. Multi-longitudinal mode operation and external doubling provide several advantages like low noise, internal modulation over a broad frequency range and variable output power. Current designs provide an output power of 20 mW, but laser has potential for higher power output.