INTRODUCTION:
Various biological samples exhibit UV-Vis reflectivity and color characteristics of interest to researchers. Applications are diverse: For example, among some species of birds, insects and reptiles, UV reflectance and color play a role in mating behavior, recognizing species and assessing predator risk. Color as an indicator of fruit and vegetable ripening is significant; also, chlorophyll distribution in crops, measured using reflectance, can tell growers something about optimum fertilizer amounts. Many more similar applications, both in the field and in the lab, can be classified as bioreflectance applications.

Jaz provides a particularly compelling option for bioreflectance applications in the field, where portability, flexibility and ease of use are critical. Jaz is a modular spectrometer-based system that integrates into a single stack those components that otherwise would have to be handled separately: the spectrometer, microprocessor with low-power display (in place of a PC), light source, battery pack and even Ethernet capability for remote measurements. Reflection probes and other sampling optics connect easily to the Jaz, keeping the overall system footprint compact and manageable.

Experimental Conditions
A typical Jaz configuration for portable UV-Vis reflectance comprises the Jaz spectrometer set from 200-850 nm, with a 25 µm slit and L2 detector collection lens. Also installed in the Jaz stack is the Jaz-B battery module, which has two slots for SD card data storage, and the Jaz-PX, a high-intensity pulsed xenon light source with up to four hours battery life on a single charge. SpectraSuite spectrometer operating software is also recommended. Depending on experiment considerations, other options to consider are the Jaz-E Ethernet module and the SpectraSuite-PAR add-on software application, which is used to calculate Photosynthetically Active Radiation (PAR) values of horticultural samples.

Most bioreflectance applications involve diffuse reflection of solid surfaces. Our fiber optic reflection/backscattering probes can measure diffuse or specular reflectance from a surface; a good choice for most UV-Vis bioreflectance applications is our QR600-7-SR/125F, a premium-grade probe with 600 µm core diameter in a six-around-one fiber configuration. Also, the probe is solarization-resistant and has a 1/8” ferrule.

Results
Bioreflectance setups using miniature portable spectroscopy have become so simple to perform that even high school science students have little problem with such setups. In one example, a student measured the reflection at 90º of philodendron plant leaves, theorizing that reflectance values could be correlated to fertilizer levels. The results suggested that plant reflectance at wavelengths >700 nm was insensitive to the stress of over-fertilization (at 4x the recommended amount of fertilizer), while the peak within the 530-630 nm range was noticeably sensitive (i.e., had greater reflectivity) to stress. The increased reflectivity related to a decrease in chlorophyll and to the effects of osmosis. Water collected between the leaf cell membrane and cell wall and exposed more of the leaf surface, which increased reflectivity.

Conclusions
The inherent flexibility of the Jaz sensing system can be exploited for a number of UV-Vis bioreflectance applications simply by mixing and matching Jaz modules and selecting sampling optics most appropriate for your application. A high-intensity, low-power pulsed xenon source and solutions to system power requirements make Jaz an extremely reliable choice for field and other measurements.

Method:
Fluorescence

Introduction:
Customer is hoping to use a probe to measure chlorophyll in water (algae) and on rocks (lichens). He currently has a USB2000-VIS-NIR and a 400 micron optical fiber. He would like to purchase a reflection probe and light source for measuring chlorophyll in situ.

Experimental Conditions:
Measurements were made with the reflection probe held in our probe holder at 90 degrees relative to the sample surface. The probe holder was placed on the leaf or lichens sample for the fluoresence measurements.

Hardware Used:
USB2000-FLG (USB2E4876)
LS-450
R400-7-VIS/NIR
RPH-1

Experimental Parameters:
Integration Time (msec): 25 – 200
Spectra Averaged: 1 – 10
Boxcar Smoothing: 3
Measurement Mode:
Fluorescence

Results:
For the leaf measurements shown in Figure 1, we were able to make measurements through glass and in water. The large peaks you see at 470 nm and 920 nm are related to the LED with the peak at 920 nm due to second order effects from the grating. Order sorting filters are not included on our fluorescence spectrometers because the filter will decrease your sensitivity to low level fluorescence. When the measurements are made through glass, there is a lot of LED light scattered back into the reflection probe.

For the lichen samples shown in Figure 2, the peaks were not as high intensity or resolved. This may be related to either the type or concentration of chlorophyll in the samples. When you compare the lichen spectra to the spectra measured for the other side of the lichen samples (bark and bark2), there are spectral differences which seem to be related to the presence of chlorophyll. When I tried to measure the lichen samples through glass, I didn’t see a lot of difference between the bark and lichen side of the sample. With the lower level of fluorescence observed for the lichen samples, we may not be sensitive enough to detect the chlorophyll in the lichen samples when we are making measurements through glass.

Figure 1:

Figure 2: