Citation: Gaitan, B.; Inglut, C.; Kanniyappan, U.; Xu, H.N.; Conant, E.F.; Frankle, L.; Li, L.Z.; Chen, Y.; Huang, H.-C. Development of an Endoscopic Auto-Fluorescent Sensing Device to Aid in the Detection of Breast Cancer and Inform Photodynamic Therapy. Metabolites 2022, 12, 1097. https:// doi.org/10.3390/metabo12111097 Academic Editor: Wesley Baker Received: 12 September 2022 Accepted: 31 October 2022 Published: 11 November 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). metabolites H OH OH Article Development of an Endoscopic Auto-Fluorescent Sensing Device to Aid in the Detection of Breast Cancer and Inform Photodynamic Therapy Brandon Gaitan 1 , Collin Inglut 1 , Udayakumar Kanniyappan 1 , He N. Xu 2 , Emily F. Conant 2 , Lucas Frankle 1 , Lin Z. Li 2 , Yu Chen 3, * and Huang-Chiao Huang 1, * 1 Fischell Department of Bioengineering, University of Maryland, College Park, MD 20742, USA 2 Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104, USA 3 Department of Biomedical Engineering, University of Massachusetts, Amherst, MA 01003, USA * Correspondence: ychen8@umass.edu (Y.C.); hchuang@umd.edu (H.-C.H.) Abstract: Breast cancer is the most diagnosed cancer type in women, with it being the second most deadly cancer in terms of total yearly mortality. Due to the prevalence of this disease, better methods are needed for both detection and treatment. Reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) are autofluorescent biomarkers that lend insight into cell and tissue metabolism. As such, we developed an endoscopic device to measure these metabolites in tissue to differentiate between malignant tumors and normal tissue. We performed initial validations in liquid phantoms as well as compared to a previously validated redox imaging system. We also imaged ex vivo tissue samples after modulation with carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP) and a combination of rotenone and antimycin A. We then imaged the rim and the core of MDA-MB-231 breast cancer tumors, with our results showing that the core of a cancerous lesion has a significantly higher optical redox ratio ([FAD]/([FAD] + [NADH])) than the rim, which agrees with previously published results. The mouse muscle tissues exhibited a significantly lower FAD, higher NADH, and lower redox ratio compared to the tumor core or rim. We also used the endoscope to measure NADH and FAD after photodynamic therapy treatment, a light-activated treatment methodology. Our results found that the NADH signal increases in the malignancy rim and core, while the core of cancers demonstrated a significant increase in the FAD signal. Keywords: optical redox ratio; breast cancer; autofluorescence; molecular endoscopic imaging; photodynamic therapy 1. Introduction In the US alone, 1.9 million people are estimated to be diagnosed with some form of cancer, with 600 thousand succumbing to the disease in 2021 [1]. Because of the risk and prevalence of this disease, accurate and early diagnoses are needed to improve pa- tient outcomes. For example, one study found early detection of breast cancer improves relative survival between 27–47% [2], and another found that a one-year survival for lung cancer drops from 85% to 15% if a patient is diagnosed at stage 4 rather than stage 1, respectively [3]. Optical imaging has gained momentum in recent years to aid in the treatment and diagnosis of cancer. One of the most popular optical imaging modalities used is fluorescence imaging due to its low cost, potentially compact size, and real-time imaging capability. This imaging modality has been leveraged to help assess various cancers. In one study, folate hapten was conjugated with fluorescein isothiocyanate to target folate receptor alpha, causing accumulation in cancerous ovarian tissue, and aiding in imaging the intraoperative ovarian cancer cells when using a fluorescent imaging system [4]. Another example is the Metabolites 2022, 12, 1097. https://doi.org/10.3390/metabo12111097 https://www.mdpi.com/journal/metabolites