Non-destructive ambient MS imaging and differentiation of fingerprints directly from a smartphone with desorption electrospray ionization (DESI)

Importance of the Topic

Mass spectrometry imaging (MSI) has revolutionized chemical mapping at surfaces but is traditionally limited to small samples. Extending ambient MSI to everyday objects like smartphones enables non-destructive, in situ visualization and chemical differentiation of latent fingerprints. This advance holds strong forensic and security implications, as well as potential applications in quality control and user authentication.

Objectives and Study Overview

The study aimed to demonstrate large-area ambient MSI of a used smartphone to visualize and chemically differentiate fingerprints from multiple donors. By combining desorption electrospray ionization (DESI) with a high-speed quadrupole time-of-flight (qTOF) mass spectrometer, the work sought to acquire high-resolution images of ridge patterns and spectral profiles across the entire device surface.

Methodology and Instrumentation

Three volunteers deposited fingerprints on a smartphone screen and performed typical touchscreen actions. The phone was mounted on a DESI XS source stage and scanned with a High-Performance Sprayer coupled to a Waters Xevo G2-XS qTOF mass spectrometer. Acquisition parameters included:

• Ionization voltage: +0.7 kV
• Scan rate: 10 Hz
• DESI solvent: Methanol with 0.1% formic acid (v/v)
• Scan area: 11.5 × 7.5 cm (86.25 cm²)
• Pixel size: 100 µm × 100 µm
• Image processing: Waters High Definition Imaging (HDI) v1.6

Used Instrumentation

• DESI XS ambient ion source
• Waters Xevo G2-XS quadrupole time-of-flight mass spectrometer
• High-Performance Sprayer assembly
• Waters HDI v1.6 software for image visualization

Main Results and Discussion

The DESI XS source imaged more than 85 times the area of a typical MSI experiment in a single acquisition (≈26 hours). High-resolution images revealed clear fingerprint ridge patterns for all three individuals. Distinct mass spectral peaks were associated with each donor, enabling chemometric differentiation. Overlay images of selected m/z values highlighted spatial distributions of molecular markers across the smartphone screen.

The ambient, non-destructive nature of DESI preserved device integrity and functionality, allowing the smartphone to be returned to the owner without damage.

Benefits and Practical Applications

This approach demonstrates rapid, large-area chemical imaging on complex objects without sample preparation. In forensic investigations, it offers a non-destructive means to capture and differentiate latent prints. Beyond forensics, similar workflows could be applied in contamination mapping, surface authentication, and quality assurance in manufacturing.

Future Trends and Applications

Advances in ion source miniaturization and portable mass analyzers will enable field-deployable large-area MSI. Higher scan speeds and finer pixel resolution may reduce acquisition times and improve image detail. Integration of machine learning for automated pattern recognition and donor identification will further enhance throughput and objectivity. Expanding the range of detectable compounds and exploring other ambient ionization methods could broaden applications across security, diagnostics, and material sciences.

Conclusion

Ambient DESI-MS imaging on a full smartphone surface successfully visualized and chemically distinguished fingerprints from multiple users. The non-destructive protocol preserved device functionality while providing high-resolution ridge patterns and donor-specific mass spectral profiles. This methodology paves the way for practical, in situ chemical fingerprinting in forensic, security, and industrial contexts.

Reference

No external literature was directly cited in the source text.