Citation: Nugroho, D.; Oh, W.-C.; Chanthai, S.; Benchawattananon, R. Improving Minutiae Image of Latent Fingerprint Detection on Non-Porous Surface Materials under UV Light Using Sulfur Doped Carbon Quantum Dots from Magnolia Grandiflora Flower. Nanomaterials 2022, 12, 3277. https://doi.org/ 10.3390/nano12193277 Academic Editors: Constantine D. Stalikas and Antonios Kelarakis Received: 23 August 2022 Accepted: 19 September 2022 Published: 21 September 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/). nanomaterials Article Improving Minutiae Image of Latent Fingerprint Detection on Non-Porous Surface Materials under UV Light Using Sulfur Doped Carbon Quantum Dots from Magnolia Grandiflora Flower David Nugroho 1 , Won-Chun Oh 2, * , Saksit Chanthai 3 and Rachadaporn Benchawattananon 1, * 1 Department of Integrated Science, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand 2 Department of Advanced Materials Science and Engineering, Hanseo University, Seosan-si 356-706, Korea 3 Materials Chemistry Research Center, Department Chemistry and Center of Excellence for Innovation Chemistry, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand * Correspondence: wc_oh@hanseo.ac.kr (W.-C.O.); rachadaporn@kku.ac.th (R.B.) Abstract: In this study, carbon quantum dots (CQDs) from Magnolia Grandiflora flower as a carbon precursor were obtained using a hydrothermal method under the optimized conditions affected by various heating times (14, 16, 18, and 20 min) and various electric power inputs (900–1400 W). Then, hydrogen sulfide (H 2 S) was added to dope the CQDs under the same manner. The aqueous solution of the S-CQDs were characterized by FTIR, XPS, EDX/SEM, and TEM, with nanoparticle size at around 4 nm. Then, the as-prepared S-CQDs were successfully applied with fine corn starch for detection of minutiae latent fingerprints on non-porous surface materials. It is demonstrated that the minutiae pattern is more clearly seen under commercial UV lamps with a bright blue fluorescence intensity. Therefore, this research has proved that the S-CQDs derived from plant material have a better potential as fluorescent probes for latent fingerprint detection. Keywords: minutiae pattern; carbon dots; latent fingerprint; nanoparticle; forensic science 1. Introduction Fingerprints are considered to be a gold standard for identifying biometrics and scientific evidence in the police field. Fingerprints are unique, and because each person has a different pattern of minutiae, they cannot be changed, unless someone gets into an accident that causes them to not have minutiae latent fingerprint, and they are easy to verify based on the capillary tube-shaped channels at the fingertips, which are connected to the sweat glands [1–8]. Fingerprint detection is currently carried out using some physical or chemical processes to detect the residue of latent fingerprint amino acids, oils, and others. This is because the characteristics of latent fingerprints cannot be seen directly by the naked eye [9–14]. Carbon dots (CQDs) are a member of the nanomaterial family, with the characteristics of a nanometer particle size, biocompatibility, low toxicity, and water-solubility. These CQDs have a photoluminescence characteristic that can be used in several applications, such as bioimaging, as drug carriers, for gene delivery, metal ion detection, sensing, and as nanothermometers. There are two methods for CQDs synthesis. The first is a top-down method by cutting the carbon source material, and it makes use of a bottom-up method involving the carbonization of small molecules. The hydrothermal and microwave method is the second method, which is a bottom-up approach possessing the advantages of energy efficiency, low cost, and convenient operation, and it is mainly used to carbonize organic matter to form luminescence at high temperatures and pressures [15–17]. In this study, we prepared an S-doped-CQDs nanocomposite material synthesized using microwave methods in various conditions to obtain the optimum product. Nanomaterials 2022, 12, 3277. https://doi.org/10.3390/nano12193277 https://www.mdpi.com/journal/nanomaterials