MDTmag.com 14 / November/December 2015 MDTmag.com
UVC LEDs: Redefining
By Hari Venugopalan, Director of Global
Product Management, Crystal IS
Lab-on-chip devices have enabled ba- sic diagnoses at the point-of-care, re- ducing the need for a centralized lab
for all analyses. Such devices range from
pregnancy and blood glucose tests in the
home, to routine analyses administered in
doctors’ offices. Advantages of lab-on-chip for the point-of-care have included
small sample volumes, rapid analysis, and
low cost. Now an even greater potential
of these devices can be realized by adopting emerging light technologies.
Lab-on-chip devices for point-of-care
applications integrate sample preparation, sample separation, signal amplification, and signal detection on a single
chip. Samples of blood, urine, saliva, or
stool are analyzed with signal detection
through electrochemical, mechanical, or
Electrochemical methods measure
differences in resistance, conductance, or
capacitance of the sample. The benefits
of these devices
include low power
of detection, and
cost, with some
sensors fabricated in
However, the shelf
life of electrodes is
severely limited by
temperature, pH, and
ionic concentration variations.
Mechanical cantilever-based devices
sense deflections or changes in resonant frequency, and can be designed to
detect specific chemical and biological
compounds. Detection of biological
compounds can be accomplished without
use of fluorescent tags (labels) which
has advantages in cost and does not use
reagents. However, these mechanical sensors typically require long analysis times
in excess of 30 minutes, and have complex
fabrication and poor detection sensitivities.
Optical detection, either by absorption
or fluorescence, is used universally in the
clinical lab with several
established methods of
detecting specific com-
pounds. It is the preferred
method because of its
robustness and sensitivity.
However, until now, optical detection has not made
the transition from the lab
to point-of-care due to the
complexity of instrumentation and the cost.
The use of intrinsic
fluorescence spectroscopy (IFS) is an example
of an optical detection
method that can further the development
of point-of-care devices.
IFS for bacterial type identification is an
emerging application in the clinical lab
and takes advantage of the fluorescence
of amino acids (tryptophan, tyrosine,
and phenylalanine) and dinucleotides
(NADH) in bacterial cells (Figure 1).
These compounds strongly absorb light
in the UVC wavelength range of 200 -
280nm and emit at longer wavelengths.
By using excitation/emission wavelength matrices, the type of bacteria in
a sample can be identified. Doctors can
then tailor therapy to treat specific infections. Using targeted treatment in place
of broad-spectrum antibiotics saves costs
and can reduce the proliferation of drug
In the clinical lab, IFS uses xenon
flash lamps, since they provide ample
UV light. However, xenon flash lamps
consume considerable power and
occupy a large footprint, making them
unpractical for IFS in point-of-care
instruments. High light output UVC
LEDs are enabling the evolution of these
devices using IFS for optical detection.
UVC LEDs are solid-state light sources
and consume less power than xenon flash
lamps (Figure 2). Additionally, power
sources for UVC LEDs are simple and
less costly than those for xenon flash
lamps. This allows for the development
of battery operated and mobile read-out
devices for deployment in doctors’ offices
or the field.
Figure 1: The excitation/emission spectrum of tryptophan.
Note that the emission signal (detection signal) is propor-
tional to the excitation intensity (light source intensity).
Figure 2: Comparison of power consumption of UVC LEDs and
xenon flash lamps.