2nd Spring Biophotonics Conference in Porto

Abstract

Following the success of the 1st Spring Biophotonics Conference in Porto [1], and in response to suggestions from numerous researchers advocating for regular exchanges of ideas, the 2nd Spring Biophotonics Conference was organized once again in the Porto area, held from June 15th to 18th, 2023. This second event gathered scientists from several countries in Europe, North America, Asia and Australia. The presentations delivered by these esteemed researchers covered a broad range of Biophotonics methods, where artificial intelligence, imaging and spectroscopy techniques were used to produce information with clinical relevance. This special issue includes a selected number of papers that resulted from the presentations made at the 2nd Spring Biophotonics conference.

The paper from Jaafar et al. describes the impact of e-cigarette liquid on porcine lung tissue [2]. Using Raman micro-spectroscopy, the authors observed that the bands intensities at 1002, 1548, 1618 and 1655 cm⁻¹ increased at five different depths after the first and second enhanced transparency treatments applied to the lung, as a result of scattering decrease at the lung surface as alveoli fill with e-cigarette liquid. A change observed in the 1937/1926 Raman band intensity ratio revealed that nicotine-free and flavor-free e-cigarette liquid induced collagen dehydration, an effect that was enhanced after the second treatment. These results show that prolonged exposure of lungs to vaping leads to collagen dehydration that can be unhealthy.

Davydov et al. use spatially resolved diffuse reflectance spectroscopy to investigate the relationship between body mass and skin hydration levels [3]. In this study skin dehydration and rehydration was monitored under various conditions, including thermal and physical loads on healthy volunteers, and in patients with edema syndrome under diuretic therapy. A correlation between body mass reduction and skin hydration was observed: 1% of body mass loss corresponds to a 10% decrease in skin hydration. The application of thermal stress results in a monotonically decrease of water absorption at 970 nm, without recovery. During physical activity, it was observed that approximately 20% of skin water was lost within 20 min, followed by rehydration. For patients with edema syndrome, a 30% amplitude decrease was observed during diuretic treatment. This study shows that a noninvasive equipment, based on optical spectroscopy, can be developed to monitor skin hydration for clinical and sports applications.

Hoffer et al. use a smartphone-based method for the detection of COVID-19 and associated pneumonia through the combination of thermal imaging and transfer-learning algorithm [4]. Thermal images acquired from the back of human individuals by a smartphone with a special camera were analyzed using a deep learning algorithm. Such method revealed a sensitivity of 88.7% and a specificity of 92.3% in the detection of COVID-19-related pneumonia.

The reconstruction of tissue absorption spectra is presented in two papers by Pinheiro et al. In the first paper, the reconstruction of the experimental absorption spectrum of rabbit lung was performed using the least squares method [5]. In this reconstruction, it was possible to obtain the concentrations for the various components of the lung: 80.00% for water, 10.20% for hemoglobin, 2.85% for DNA, 2.35% for proteins, and 2.30% both for melanin and lipofuscin. The equal accumulation for the melanin and lipofuscin was associated with the ageing of the lung.

Applying the same method, Pinheiro et al. also reconstructed the absorption spectra of human kidney tissue in both healthy and chromophobe renal cell carcinoma (CRCC) cases [6]. In this study, by assuming that both types of kidney tissue have the same water concentration (77%), it was possible to calculate the differentiated concentrations for DNA, oxygenated and deoxygenated hemoglobin, proteins, lipids and pigments. Gathering these results, it was observed that the concentration of oxygenated hemoglobin increases about 60%, while the concentration of deoxygenated hemoglobin decreases to approximately 1/3 from the healthy to the diseased kidney. The concentration of DNA almost doubles from the healthy to the diseased kidney, while the concentration of proteins is almost 3× higher in the presence of CRCC. The concentrations of lipids in both version of the kidney tissues are less than 1%, but such value in the CRCC kidney is about 6× higher than in the healthy kidney. Regarding the concentrations of pigments, both kidney tissues show higher contents of lipofuscin than melanin, but a comparison between these values shows an apparent conversion of melanin into lipofuscin as a result of the formation of melanolipofuscin granules when cancer develops. These results show that the estimation of such differentiated concentrations can be done in vivo for diagnostic purposes through the application of machine learning algorithms to diffuse reflectance spectroscopy measurements for the reconstruction of the absorption coefficient spectrum.

Moldon et al. use optical clearing agents to monitor the changes of the scattering properties of human nail bed and blood microrheological properties [7]. Using in vivo OCT and optical digital capillaroscopy measurements, it was found that the application of optical clearing agents significantly increases and enhances the visualization of the nail bed, through the reduction of light scattering and improvement of light refraction. Clearer images were possible to acquire from deeper layers of the nail bed. By refining the optical clearing protocol, it may become possible to use this technique to enhance various methods for capillaries visualization and evaluation of blood perfusion. By performing ex vivo experiments, where blood samples were incubated with glycerol, it was found that this agent reduces RBC aggregation and RBC deformation and increases intracellular viscosity. All these results are valuable for future applications where the evaluation of blood microrheology modifications is necessary.

Sokolowski et al. present a novel spectroscopy method supported by machine learning for real time detection of infectious agents in wastewater [8]. Although still in a prototype version, with a prediction accuracy of 68%, this method can already be used for real time detection of the presence of inflammation biomarkers in wastewater, such as the proposed C-reactive protein. The proposed method is universal and after improving the prediction model, it can be used in epidemic situations or in public facilities, such as schools or hospitals to perform early detection of infectious agents and prevent the broad spreading of diseases.

Zhang et al. use the probing polarization response of monolayer cell cultures with photon pair entanglement for sample morphology discrimination [9]. The authors report that a differentiated response was obtained, both between the cell culture sample and the host medium and between two types of monolayer cell cultures. This was the first experimental study to enable monolayer cell culture differentiation using a polarimetry-based method, but as reported by the authors, the method has a great potential for future developments and applications for cell analysis and differentiation.

The editors would like to express their deepest gratitude to the authors that contributed to this special edition and hope that these articles will be of interest to the Biophotonics community and to clinical professionals.

We are looking forward to the next Spring Biophotonics conference in Porto.