BioPhotonics Preview - March/April 2022

Light Sources and Microscopy

The light source of a widefield fluorescence microscope is often overlooked by scientists setting out to capture fast cellular processes with live-cell imaging, but LEDs have changed the game. Thanks to innovations such as multi-wavelength systems, TTL triggering, and inline excitation filters in Pinkel configurations, expensive motorized equipment is not always needed. Another benefit to these latest technologies is the ability to reduce phototoxicity and therefore provide more accurate and insightful data and this article will also explain how.

Hyperspectral Imaging and Blood Oxygenation

The measurement of oxygen levels in the blood commonly referred to as blood oxygen saturation (SpO2) is a critical medical diagnostic. The condition of below normal levels (<95%) is termed hypoxemia and is associated with patients who have asthma, heart disease, and chronic obstructive pulmonary disease (COPD), anemia, interstitial lung disease, emphysema, acute respiratory distress syndrome or ARDS, pneumonia, obstruction of an artery in the lung (due to a blood clot, pulmonary fibrosis or scarring and damage to the lungs). SpO2 is monitored when levels drop sufficiently low that cyanosis occurs, indicating there is a threat to life. However, monitoring of SpO2 levels are also of interest for brain and other surgical procedures (i.e. flap surgery), peripheral vascular disease (PVD), tumor development, the healing of wounds from conditions such as diabetic foot ulcer, systemic rheumatic disease, neuropathy and sepsis2–5. Pulse oximeters, a simple optical device that measures the ratios of two critical band-passes of light through an appendage, typically the patient’s fingertip, is the current conventional method of measuring SpO26. This device provides an approximate average reading of blood oxygenation for the entire body. It does not provide information of local distribution. Hyperspectral imaging cameras generate ‘hyper-cubes’ or data-cubes of data, whereby the spectrum at each pixel in the image is collected. Subtle reflected color differences that are not observable by the human eye or even by color (RGB) cameras are immediately identifiable by comparison of spectra between pixels. A variety of spectral imaging technologies exist.

Photoacoustic Remote Sensing Microscopy

Remote Sensing (PARS) microscopy provides optical absorption contrast; however, unlike other photoacoustic imaging modalities, it functions without contact. In this article we discuss:

(1) Invention and mechanism of PARS microscopy, benefits and challenges, and future directions.

(2) PARS for Histology. How and why PARS can distinguish cancerous from non-cancerous tissues during surgery. PARS microscopy could help ensure that healthy tissue remains intact while all cancerous tissue is removed, potentially eliminating the need for multiple surgeries. We will highlight our latest developments including PARS-OCT for 3D histology and real-time histology-like imaging in several human tissue types.

(3) PARS for Ophthalmology. How and why PARS can help doctors diagnose and treat blinding diseases earlier than is now possible. We will show our latest development of PARS for ophthalmology applications: PARS-OCT imaging modes.

Trends in Microfluidics

Miniaturization of optofluidics technology has made possible the transportation of a diagnostic system – which contains a channel, light source, micropump, and biomarker identification – to the bedside. But some of the components (such as a laser, for example) can be hard to shrink enough in dimensions to put on a chip and still be effective. So companies that are producing microfluidic chips for cell analysis, for example, have focused their energies on miniaturizing as much as they can with other instrumentation (such as the laser) placed in a clinical or hospital setting. Recent developments, however, have taken this technology to the next level, imprinting multiple biomarkers on a microfluidic channel in a disposable chip which can then be activated by a simple and small laser design in a box, producing results in a short amount of time along parallel channels. Some examples have been placed in veterinary medicine and water testing. This technique has drawn increased attention with the need for rapid diagnosis of transmissible diseases such as COVID-19. In the wake of changes in technology, there is a major push in the industry for testing standards during production, and organizations like the Microfluidics Association are working toward a solution.