Fabrication of a Low Cost Superhydrophobic Substrate for Surface Enhanced Laser-Induced Breakdown Spectroscopy and Its Utility through Identification of Electrolyte Variation for Oral Cancer Detection

Abstract

Ultratrace elemental detections from a limited volume of samples can offer significant benefits in biomedical fields. However, it can be challenging to concentrate the particles being analyzed in a small area to improve the accuracy of detection. Ring-like deposits on the edges of colloidal droplets are a vexing problem in many applications. Herein, we report ultratrace elemental detection using a superhydrophobic surface-enhanced laser-induced breakdown spectroscopy (SELIBS) substrate fabricated by laser ablation followed by a soft lithography technique. In this work, the SELIBS spectra on a superhydrophobic polydimethylsiloxane (PDMS) substrate replicated from a laser-patterned master Teflon substrate are investigated. This work highlights the application of this newly created superhydrophobic substrate for detecting trace elements in body fluids using SELIBS. The developed PDMS substrate was successfully adopted to investigate the electrolyte variation in serum samples of oral cancer patients and normal volunteers. Principal component analysis (PCA) and match-no-match analysis were used to distinguish the elemental variation in cancer and control groups.

Keywords: SELIBS; biomedical sensing; nanostructured material; oral cancer; superhydrophobic PDMS.

Figure 1

Schematic diagrams of the microreplica nanopatterns on PDMS film.

Figure 2

(a) SEM images of original PDMS and the patterned Teflon replica of PDMS and corresponding contact angle images; (b, c) evaporation of droplet on the bare and engraved Teflon replica of PDMS PDMS.

Figure 3

LIBS spectra of 100, 600, and 100 ppb Cu, Cd, and Pb on bare and patterned PDMS substrates. Inset: comprehensive comparison with the LIBS signals on the newly proposed superhydrophobic PDMS substrate with bare PDMS substrate to demonstrate the advantages of the new method using 100 ppb Cu.

Figure 4

Calibration graphs of Cu, Cd, and Pb with the superhydrophobic PDMS substrate.

Figure 5

LIBS spectra of a blood sample using drop coating deposition

Figure 6

(i, iii) LIBS serum spectra indicating Ca and Cu variation in normal and oral cancer cases and (ii, iv) principal component analysis (PCA) for normal and diseased subjects – Ca, Cu variation.

Figure 7

Mahalanobis distance vs spectral residual for an oral cancer standard set.