When miniature spectrometers were introduced in the 1990s, they benefited from a perfect storm of technological circumstances:
• The development of detectors for mass-volume markets, which lowered system costs dramatically and allowed designers to make the instrument footprint much smaller than with traditional instruments
• The evolution of personal computers, which allowed spectrometers to process high-speed, high-resolution spectral data
• The growth of fiber optics, making it much easier to bring the spectrometer to the sample
Unlike many disruptive technologies, miniature spectroscopy never replaced the traditional technology — in this case, laboratory benchtop spectroscopy. Instead, miniature spectroscopy became its own technique, and in many cases, complementary to the spectroscopy technologies of the day.
Advances in detectors, optics, and electronics bring the power of spectral sensing to a wide range of field applications.
As spectrometers have become even smaller, faster and more powerful, applications once considered impractical outside the laboratory are feasible. For example, expensive laboratory spectrophotometers have been used to monitor the color or chemical composition of a finished product. Now, multiple spectrometer modules can be installed into process lines for measuring quality characteristics.
They can also be transported into the field for applications such as assessment of crop growth or monitoring of environmental parameters.
Smaller, lower-cost spectrometers and optical benches are ideal for integrating into other analytical devices. The emergence of a more sophisticated generation of CMOS detectors, more commonly associated with cell phone and digital camera imaging needs, has provided a viable alternative to CCD array spectrometers for various spectroscopy applications. CMOS detector-based spectrometers are truly micro-sized -— in some cases less than 2 inches square — and can weigh just a few ounces.
This is very attractive for manufacturers seeking the power of multiple wavelength spectral analysis with the size and cost criteria more commonly associated with single-wavelength and comparable analytical devices.
As a result, CMOS detector-based microspectrometers have become more desirable for original equipment manufacturers (OEMs) and high-volume applications where one or more wavelengths are being monitored and customers seek a highly reproducible result.
Life sciences, medical diagnostics, solid-state lighting, and environmental analysis are among the industries where microspectrometers are an alternative to filter-based optical sensing systems and single-wavelength devices.
More than just a spectrometer
Today’s CCD-array miniature spectrometers are often more than just a spectrometer. Components such as light sources and batteries can be attached to the spectrometer, forming a monolithic instrument. Also, because accessories have evolved to complement the portability of miniature spectrometers, low-power sources and streamlined sampling optics are readily available.
Micro-sized spectrometers utilize CMOS-detector technology to provide full-spectrum capabilities.
Most important, microprocessors and displays can replace laptop PCs, and adding wireless and similar capabilities to transmit data from the field is well within reach.
Smaller, fiber-coupled spectrometers are ideal for field measurements of all kinds, from monitoring the amount of light absorbed by phytoplankton or fluoresced by corals to measuring the reflectance of bird plumage or reptile skin to better understand the nature of color-based mate selection. Also, color as an indicator of fruit and vegetable ripening is significant, as is chlorophyll distribution in crops, where reflectance measurements help growers assess optimum fertilization.
Although near-infrared spectroscopy has not yet become as compact and affordable as ultraviolet-visible spectral technologies, alternatives to indium gallium arsenide (InGaAs) detectors have emerged that show promise. Still, today’s InGaAs systems are used outside the lab for inline applications such as protein and moisture analysis of whole, ground, and processed grains and analysis of starch and sugar (primarily fructose, glucose, and sucrose) as an indicator of fruit maturity and quality.
NIR spectroscopy is a powerful measurement tool for the characterization of agricultural samples. With no requirement for sample preparation and long NIR wavelengths where absorption is weak, NIR measurements allow sampling through the peel of the fruit. Differences in NIR diffuse-reflection spectra for peeled and unpeeled fruit arise from a combination of phenomena including the amount of light scattered from the surface of the fruit and the penetration depth of the NIR light into the sample (See Fig. 1).
Figure 1. Differences in NIR diffuse-reflection spectra for peeled and unpeeled mango. NIR spectroscopy is a useful tool for measuring starches and sugars as an indicator of fruit quality.
When noninvasive sampling is coupled with the ability to make rapid measurements, NIR analysis is a great option for online measurement of fruit by growers and packers to ensure they are shipping quality produce to their customers.
Raman analysis is another powerful technique benefiting from developments inspired by a growing market demand. Raman provides a practical solution for non-destructive chemical identification across a range of markets including pharmaceutical processing, forensics, law enforcement, and homeland security.
For many years, Raman was a cumbersome, expensive research tool relegated to laboratories. But today’s economical, compact lasers and detectors make Raman spectroscopy possible in a handheld format — a quantum leap forward. The notion of using a sort of “Raman engine” (compact laser, spectrometer, and microprocessor) in a customized handheld device with built-in chemometric capabilities is within reach.
The refinement of existing technologies and the development of new ones have combined with improvements in engineering and manufacturing processes to rapidly lower the cost to make products and distribute them. The next generation of optical sensing technologies will offer a framework for the creation and testing of new business models based on the distribution of knowledge and service. In fact, this concept of “distributed sensing” has already emerged in networked systems monitoring various aspects of the environment.
New distributed sensing models
It’s not too difficult to imagine a scenario where instruments become a community of independent modules that communicate. The communication can occur within the instrument and its subordinates — secondary channels in a multichannel spectrometer setup, for example — or among other instrument modules that are plugged in anywhere on the Internet.
The communities can be a few modules, as in a typical spectrophotometric experiment like measuring absorbance of a sample in a cuvette, or the communities can be large and very distributed.
The smart instrument modules of the network form an infrastructure upon which information can be shared and businesses can be built. The value resides in the network itself, not the piece. Think of all the folks developing applications for the iPhone and iPod touch.
Forward-thinking companies in all sorts of technology industries won’t be focused solely on designing and distributing better MP3 players or cell phones, for instance, but in creating methods for distributing the information those devices capture, display, and store.
For spectroscopy to continue to advance outside the lab, such distributed sensing models are likely to emerge.
–Rob Morris is director of marketing for Ocean Optics. He has nearly 20 years of sales and marketing experience in the photonics industry, and he has co-authored dozens of technical articles, including for the SPIE Newsroom. He has a journalism degree from Pennsylvania State University.
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