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Pharmaceuticals and diagnostics continue to represent the two largest segments of the nearly $50 billion global analytical and life sciences instrumentation market. This is in large part due to increased healthcare spending resulting from an aging population, as well as the fast-growing demand for personalized medicine.
Increased need for point-of-sample analyses is also driving the development of portable analytical instruments—devices that will, in many instances, move traditional quantitative analyses out of the laboratory and into the field. Compact, and in some cases battery-operated, these instruments will give users the freedom to perform spectroscopic measurements/analyses where and when needed.
The following case studies are indicative of how life sciences instrument designers are developing the next generation of smaller, UVC LED-based portable devices (Crystal IS, Green Island, N.Y.). Each example demonstrates how UVC LEDs can replicate and in some cases exceed the performance of their larger, more expensive lamp-based counterparts.
Measuring concentration and purity of DNA samples
DNA measurement devices that can be used in a lab or workplace—for instance, crime scene forensics—were among the first UVC LED-based instruments developed for a specific life sciences application. The process of extracting and purifying a cell’s DNA is critical in the biotechnology and forensics fields. As the first step in the analysis and manipulation of DNA, extraction/purification allows scientists to detect genetic disorders, produce DNA fingerprints and create genetically engineered organisms that produce insulin, antibiotics and hormones.
Quantitative analysis of DNA concentration and purity is based on UV absorption spectroscopy. Both DNA and protein absorb UV light, but at absorption peaks of 260 nm and 280 nm, respectively. The absorbance at each wavelength determines the concentration of DNA and protein, respectively, while the ratio of the absorbance determines the purity of the DNA sample.
Xenon flash lamps are the traditional UV light measurement source because they deliver sufficient intensity at the relevant wavelengths. However, xenon flash systems tend to use array detectors, which increase the system cost. While xenon flash lamps generate light across multiple wavelengths, DNA purity is determined by absorbance measurements taken at 260 nm and 280 nm, so filters and mirrors must be used to filter out unwanted spectra. Relatively high voltage sources and increased electronic shielding during lamp ignition also add to the system cost and complexity.
As an alternative, UVC LEDs have a smaller footprint, and can turn on/off instantly to support portable battery-powered designs with a lower cost of ownership. The high LED light output also delivers a lower, more precise detection limit for DNA measurements. and the high spectral quality of the LED leads to linearity of measurement over three orders of magnitude of concentration from 0.5 to 2000 ng/μL (Figure 1).
Figure 1 – Plot of absorbance at 260 nm versus concentration of double-stranded DNA (dsDNA) demonstrating excellent linearity over vastly different levels of concentration.As a result, portable DNA measurement systems using UVC LEDs are now being widely adopted. These devices are able to match and sometimes exceed the performance of lamp-based systems, while delivering higher efficiency and reduced costs.
Detectors for liquid chromatography
LEDs are also driving the development of portable instruments in liquid chromatography. Chromatography instruments are used for protein purification, routine process monitoring in pharmaceutical and beverage manufacturing, quality control and biotechnology research. These instruments typically employ absorption spectroscopy with a deuterium lamp to detect and analyze a range of compounds.
Conventional benchtop HPLC systems have a relatively large footprint. Until recently, the dimensions and weight of each functional component in LC systems, including the detectors, has hampered development of portable LC systems.
Smaller columns and microfluidic components can help increase sensitivity and portability, while also reducing system size, solvent consumption and waste and, thus, overall cost of ownership. But it is equally important to reduce the size and weight of the detectors.
Today, UVC LEDs are being used to develop new, portable detectors for chromatography. Designers at Marion Research (Lenexa, Kan.), for example, have created a portable detector that exceeds the performance of traditional fixed-wavelength detectors, but at less than half the cost, and less than one-tenth the size and weight. Further, the system requires 90% less power.
While traditional HPLC systems employ high-end deuterium lamps to deliver a very stable light output, UVC LEDs are even more stable. Short-term light fluctuations (indicating extent of light stability) from UVC LEDs have been measured at 0.002% or lower, while the same measure for deuterium lamps ranges from 0.005 to 0.05% (Figure 2). The UVC LEDs also provide higher light intensity, enabling the use of inexpensive silicon photodiodes as detectors.
Figure 2 – Comparison of light output fluctuation between an aluminum nitride (AlN)-based UVC LED and a high-end deuterium lamp. Peak-to-peak fluctuation within each 30-second interval is measured and averaged over a 15-minute time frame.To eliminate noise, the Marion Research detector modulates the light with a synchronous multiplexer. This allows the detector to measure differentially between the dark (zero) and light states. With a UV lamp, modulation requires a physical shutter, which is more expensive. LEDs, on the other hand, turn on instantaneously and their output can be controlled by modulating the current.
The baseline noise of the detector—a measurement of the detection limit—was evaluated for the lattice-matched Optan LED (Crystal IS), and was found to be lower than the noise value with a deuterium lamp in similar systems (see Table 1). This is due to the improved stability of light ALoutput from the UVC LED, as shown in Figure 2. The drift of the LED-based detector is also lower compared to the deuterium lamp system. This is due to the relatively lower sensitivity of light output with temperature for the LED and the use of the synchronous multiplexer.
Table 1 – Comparison of the baseline noise and drift between Optan LED and deuterium lamp detectors
The detector was then coupled to an HPLC setup and separation performance was evaluated using standard solutions, with detection at 255 nm. The results revealed that, at the optimum detection wavelength, the system is able to provide an acceptably high sensitivity. In addition, there is no noticeable drift and the baseline noise is relatively low.
Similar to the DNA purity measurements discussed previously, many chromatography applications require only one or two fixed wavelengths. Traditional deuterium lamps offer a broad spectrum of wavelengths—but much more than is usually needed. Because of the LED’s near-monochromaticity, Marion designers were able to eliminate monochromators or filters and simplify the optical design. The UVC LEDs also enabled the use of less bulky, inexpensive LED drivers, thereby keeping the footprint relatively small.
The detector, which is designed for wavelength applications in the 250–280 nm range, thus exceeds the performance of traditional deuterium lamp detectors at less than half the cost and a substantially smaller footprint (44 mm diameter by 44 mm long). These portable detectors are now being used by manufacturers to develop new, miniaturized liquid chromatography systems for point-of-care diagnostics and also environmental analysis in the field—which will help users avoid sample decomposition during transport while also reducing analysis time and cost.
Summary
With demand on the upswing, analytical instrument designers and manufacturers continue to focus on the development of smaller, lower-cost, portable instruments for point-of-sample analyses. Many of these instruments require functional components with a smaller footprint that are also lighter and capable of battery operation.
The relatively higher light intensity, near-monochromaticity, low power consumption and small footprint of LEDs enable the development of lower-cost, smaller-footprint, lightweight analytical instruments. With overall spending on analytical instruments continuing to rise, experts agree that many purchases will involve a new generation of portable UVC LED-based instruments that will move time-consuming diagnostic processes out of the lab and into the field.
Dr. Hari Venugopalan is the director of global product management for Crystal IS, 70 Cohoes Ave., Green Island, N.Y. 12183, U.S.A.; tel.: 518-271-7375; e-mail: [email protected]; www.cisuvc.com