1：Experimental Design and Method Selection:

The study utilized a homemade electrospray deposition device to deposit TiO2 nanoparticles onto latent fingerprints for physical enhancement and as a matrix for MALDI MSI analysis. Fourier transform ion cyclotron resonance (FTICR) mass spectrometry was employed for high-resolution chemical analysis and imaging.

2：Sample Selection and Data Sources:

Latent fingerprints were collected from volunteers on various surfaces including ITO-coated glass slides, metal, plastic, tape, and varnished wood. Sebaceous oil-rich and doped fingerprints (with hand cream) were specifically prepared.

3：List of Experimental Equipment and Materials:

TiO2 nanoparticles (Sigma-Aldrich), DHB matrix (Lancaster), methanol, acetonitrile, ultrapure water (Millipore), ITO-coated glass slides (Bruker Daltonics), scanning electron microscopy (SEM JEOL 6701), iPhone 6s Plus for photography, Bruker solariX mass spectrometer with SmartBeam laser optics.

4：Experimental Procedures and Operational Workflow:

Fingerprints were deposited on surfaces, TiO2 NPs were electrospray deposited using optimized parameters (e.g., 4 kV voltage, 1 mm/s stage speed), followed by MALDI MSI analysis in positive ion mode with specific laser and voltage settings. Data were processed using Bruker software.

5：Data Analysis Methods:

High-resolution MS spectra were analyzed using HMDB and LIPID MAPS databases with a mass error of 5 ppm. MS/MS spectra via CID were used for structural confirmation. Imaging was performed with FlexImaging software using RMS normalization.