Yvette Mattley, PhD

Both Raman and infrared spectroscopy techniques have been used to characterize textiles and fabrics for incoming inspection of raw materials, and to assess the authenticity of products produced from these materials. In the case of colorful textiles and fabrics, infrared spectroscopy is sometimes preferred to Raman to avoid the strong Raman background spectrum that can arise from the dyes found in brightly colored textiles.

Reflectance from 100% cotton, nylon, and satin textile samples was measured across the extended near-infrared (NIR) wavelength range (1350–2500 nm) using the Ocean Insight NanoQuest spectral sensor with a high-powered tungsten halogen light source and 600 µm visible-NIR reflection probe. Measurements were made with the probe oriented at 90 degrees relative to the fabric surface using a manual optical stage. All measurements were referenced to a PTFE (Teflon) diffuse reflection standard.

NanoQuest is based on Fourier transform infrared (FT-IR) technology. Its patented micro-electro-mechanical systems (MEMS) technology allows for a continuous-wave Michelson interferometer to be created monolithically on a MEMS chip, enabling detection of all wavelengths simultaneously across the 1350–2500 nm range.

In the NanoQuest software, optical resolution was set to 8 nm (FWHM) and a custom gain setting was generated to optimize the signal-to-noise ratio for the measurement setup. Each sample was measured at five different locations with resulting spectral data pretreated by a second derivative with smoothing, and a standard normal variate (SNV) was applied. Principal component analysis (PCA) was applied to the dataset.

The NIR spectra measured with the NanoQuest can easily discriminate among the different textile types. Figure 1 shows the reflectance spectra of the three textiles measured: cotton, nylon, and satin. Differences in the spectral profile for each sample can be seen readily, and the inset PCA plot shows distinct separation between the clusters for each textile sample.

 Comparison of three textile samples measured with NIR reflectance. The inset PCA scatter plot shows results after pretreatment by 2nd derivative and SNV.

The experiments clearly demonstrate that NIR spectra measured with the NanoQuest have unique features helpful to identify both natural and synthetic textiles. Application of PCA to the spectra further demonstrated the distinction among textile samples. Additional investigation may include testing unknown textile samples to correctly identify them.

In addition to authentication of textiles, polymers, and other materials, NanoQuest application areas include food and agriculture (soil analysis and soybean screening) and biomedical and life sciences (bodily fluids analysis).


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Articles

FT-NIR spectroscopy is a useful tool to identify textile samples, with distinct spectral features observed at wavelengths >1350 nm. This approach can be applied to authentication of natural and synthetic consumer textile products.


Identifying Textiles with Extended-Range  NIR Spectroscopy 

As a premium-priced, all natural product, honey is sometimes adulterated with substances such as sugar syrup, molasses, starch, and water to fool the consumer with a finished product that is less than pure. Detecting adulterated honey is a challenge due to natural variations in composition arising from nectar differences. Additional variability is added via processing and storage conditions. 

	As research has demonstrated, fluorescence measurements are ideal for a rapid screening of honey samples because fluorescence is nondestructive and simple to perform. Little to no sample preparation is necessary and testing does not require complicated instrumentation or highly trained personnel.

-FL spectrometer and a 365 nm LED as the fluorescence excitation source. Fluorescence spectra were measured for several different types of honey, including clover honey, golden blossom honey, orange blossom honey, and organic honey.

	Undiluted honey was pipetted into a disposable cuvette and placed in a 4-way cuvette holder with the excitation and emission fibers arranged at 90 degrees. The fluorescence spectra measured for the honey samples (measurement time was kept constant for all the samples) are shown in Figure 1. Differences in fluorescence intensity and subtle differences in spectral shape are observed for all of the samples.


	Figure 1: Fluorescence of pure honey with 365 nm excitation. The spectra are dominated by fluorescence response due to the flavonoids present in the honey.

	The broad fluorescence peak observed between 400–700 nm in each spectrum results from the presence of flavonoids (antioxidant compounds) in the sample. Variations in the shape of these fluorescence spectra are attributed to differences in the flavonoid composition of the nectar used in the honey. The small peak at 365 nm is not fluorescence from the honey but excitation energy that is scattered into the spectrometer by the undiluted, optically dense honey samples.

	The flavonoids that dominate the fluorescence spectra for honey shown in Figure 1 are polyphenols. These plant metabolites determine the color, aroma, and flavor of the honey, and provide antioxidant and other health benefits. The fluorescence spectrum for each honey sample illustrates the sensitivity of fluorescence spectroscopy for characterizing honey.

	The measurements we conducted focused on the fluorescence of a small set of pure honey samples using a single excitation wavelength. Additional measurements could be performed by mixing and matching our modular spectroscopy components. For example, we could use a range of LEDs for fluorescence excitation to find the optimal excitation wavelength for the detection of honey adulterants.

	Regardless of our approach, through the use of modular spectroscopy components, measurements can be taken out of the laboratory setting to test honey quality during bottling or at the point of sale to authenticate that the honey is pure.


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The flavonoids that dominate the fluorescence spectra for honey shown in Figure 1 are polyphenols. These plant metabolites determine the color, aroma, and flavor of the honey, and provide antioxidant and other health benefits. The fluorescence spectrum for each honey sample illustrates the sensitivity of fluorescence spectroscopy for characterizing honey.

Fluorescence Spectroscopy Detects Adulterated Honey

Although most often associated with Christmas, multicolored holiday lights are used year-round as an appealing decorative accent. Today, LED lights are as ubiquitous as incandescent lights, with manufacturers touting their low power requirements, high efficiency, and bright color. But how do LEDs compare with incandescent decorative lights? Here's what we discovered when measuring the relative irradiance of several multicolored light strings.

Experiment Materials and Spectrometer Setup

	We tested one string of 20 multicolored incandescent lights and two strings of multicolored LED lights - one was a new, 10-light string and the other was a slightly used, 20-light string. The incandescent lights were purchased at a local pharmacy for about $4 and the newer LEDs for $5 (for half as many lights). All the lights were manufactured in China.

	Our measurement setup comprised a spectrometer (200–1025 nm), an integrating sphere, an optical fiber, and spectroscopy software. We used a radiometrically calibrated light source as the reference and measured the incandescent lights and newer LED lights straight from their packaging and the older LEDs on a "tree" fashioned out of laboratory clamps and fittings.

	The incandescent lights that we measured had broadband spectra with very strong intensity in the shortwave NIR region >700 nm (Figure 1). The light at these wavelengths produces heat, which makes the bulb warm during operation.


	Figure 1: In incandescent lights, heat results from the spectral output at wavelengths >700 nm.

	The LED light strings that we measured had narrowband emission with no intensity in the shortwave NIR region >700 nm, which allows the bulbs to remain cool to the touch even after long periods of operation. In addition to producing less heat, the LEDs are more energy efficient than incandescent lights.

	Generally, the LEDs produced brighter colors than the incandescent lights, especially in the blue and green bulbs (Figure 2).


	Figure 2: The LED bulbs had strong output for the colors tested, especially at blue and green wavelengths.

What Can Relative Irradiance Measurements Reveal?

	The spectrometer setup used for these measurements showed good results for the incandescent and LED lights tested, providing some insight into the differences between the two types. Variability in performance between the LED strings also was observed. Our experiment suggested that the LEDs perform very well spectrally, although to make an assessment of cost effectiveness versus incandescent lights would require additional testing and analysis.


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Although most often associated with Christmas, multicolored holiday lights are used year-round as an appealing decorative accent.

Yvette Mattley, PhD

Articles

Identifying Textiles with Extended-Range NIR Spectroscopy

Fluorescence Spectroscopy Detects Adulterated Honey

Relative Irradiance of Decorative Incandescent and LED Lights