Responsive polymers are used in drug delivery, switchable biocompatible coatings, and advanced bio-interfaces in bioanalytical devices. Thermo-responsive polymers, where changing the temperature stimulates changes in the polymer properties, are the most common in biomedical applications. All thermo-responsive polymers have a lower critical solution temperature (LCST). Above or below this temperature determines the state of the polymer.

The use of imaging and free-space optical communication is increasing in underwater applications. Optical communication and inspection of piers, pilings, or ship berthing areas requires overcoming the constantly changing characteristics of the water, especially in the ocean. Researchers from the Naval Information Warfare Center Pacific (U.S.) and the University of Central Florida have designed and developed new algorithms and a portable scintillometer to characterize ocean turbulence for imaging and free-space optical communication applications. Suspended particulates scatter light and organic material absorbs light in the ocean, but ocean turbulence can limit resolution of imaging due to temperature gradients (thermocline) or salinity. As turbulence is not constant in relation to water depth, a real-time characterization of turbulence conditions is needed. With this design, the refractive-index structure parameter (C_n²) and the inner scale of optical turbulence (ℓ₀) were measured at 1.9 x 10^-11 m^-2/3 to 2.3 x 10^-10 m^-2/3 and 0.1 to 0.3 mm, respectively, correlating to measured thermocline parameters.

Laser absorption spectroscopy is built upon the properties of the Beer-Lambert Law, in the most basic form, relating the absorption of light and the concentration of a particular gas. Researchers from China have developed a new concentration inversion model for wavelength modulation spectroscopy (WMS) techniques in tunable diode laser absorption spectroscopy (TDLAS) applications. Traditional models do not take into account variations of the modulation depth in the second harmonic signal of the laser, thereby increasing the error of the measurement and decreasing the accuracy of the system. Through simulations and controlled experiments measuring CO gas concentrations, researchers achieve root-mean-square error (RMSE) of the gas concentration measurements of 5.468 × 10-5 with relative error of < 0.37% using an improved model of concentration inversion with modulation depth as a variable parameter. This model produces almost an order of magnitude better RMSE and almost five times better relative error, making this applicable in fields such as industrial and environmental gas monitoring.

Functional imaging of tumor cells provides critical information about the size and location of the tumor, as well as the micro-environment. Many tumors grow faster than blood vessels can form, leading to a lack of oxygen. HIF-1α then regulates the creation of new vascular networks. Hence HIF-1α can be used to identify tumor aggressiveness, proliferation, and likelihood to metastasize. Researchers from Spain have reported a fluorescent hypoxia biosensor based on the oxygen-dependent degradation domain of HIF-1α. This probe is stabilized under hypoxia, properly degrades under normoxia, and retains the oxygen sensing capability of HIF-1α. The developed hypoxia sensor contributes to a deeper view and understanding of the tumor micro-environment that modern imaging techniques cannot provide.

Due to the highly sensitive nature of fluorescence spectroscopy, the spectra were recorded with a fluorometer coupled to Wavelength Electronics’ LFI-3751 temperature controller. The high performance and high precision LFI 3751 temperature controller ensured stable wavelength and power of the emitted light.

The complete case study is available as CS-TC05.

Gas emissions from large-scale livestock facilities increase directly with operation growth due to animals’ breath, waste fermentation, and the physical decomposition of the waste.

Researchers from China have developed a laser absorption spectrometer for high precision ammonia gas detection in livestock and poultry housing. Two different techniques are discussed: Open path laser absorption spectroscopy (OPLAS) and tunable diode laser absorption spectroscopy (TDLAS). Both provide support for precision air quality detection and control for this application. TDLAS achieves ammonia detection concentrations of lower than 5 ppm using harmonic absorption signals in the long path gas absorption well with total path length traveled for the light around 4.3 m. Laser absorption spectroscopy has similar results to other gas detection methods, while providing rapid and precise gas detection in portable systems.

Detecting biomolecules, such as proteins or cells, with precision and high sensitivity is labor intensive with traditional assay devices. Researchers from the United Kingdom have developed a virus laser for rapid biomolecular detection with the precision of commercial systems. The commercial feasibility and low manufacturing cost of a genetically-engineered Tobacco Mosaic virus-like particle (rTMV) is investigated for virus laser applications, and the detection limit and amplified lasing signal are quantified for a virus laser utilizing the rod-like virus, M13.

In laser modulation, the current or voltage varies with time to modulate the output signal from the laser.  This can be accomplished in two ways: by changing the signal input/driving current or by alternating the continuous wave output after the light is generated.  This Application Note discusses both methods and provides troubleshooting tips for each.

The complete Application Note is available as AN-LD19.

Researchers have developed a polymerase chain reaction (PCR) thermal cycler using a proportional-integral (PI) temperature controller. The precise temperature controller is needed for stable temperature control and rapid temperature changes in the PCR process. The portable and low-cost thermal cycler allows better opportunities for low-resource areas compared to the bulky and expensive commercial devices available. The developed system produces a temperature ramp rate of 5.5ºC/s at a proportional gain value of 15 A/V and an integral gain value of 1.8 A/V. 

Researchers at Northwestern University, Illinois have designed a terahertz (THz) frequency comb using a Quantum Cascade Laser (QCL) with a Distributed Feedback (DFB) grating inside the cavity. The DFB grating addition allows for dual wavelength emission from the QCL. A single-mode state and a harmonic comb state combine inside the cavity for a THz frequency comb. Two uses of QCL frequency combs demonstrated by researchers at Harvard University are also discussed.