Ultrafast Laser-Ablated Nanoparticles and Nanostructures for Surface-Enhanced Raman Scattering-Based Sensing Applications

Summary

Ultrafast laser ablation in liquid is a precise and versatile technique for synthesizing nanomaterials (nanoparticles [NPs] and nanostructures [NSs]) in liquid/air environments. The laser-ablated nanomaterials can be functionalized with Raman-active molecules to enhance the Raman signal of analytes placed on or near the NSs/NPs.

Abstract

The technique of ultrafast laser ablation in liquids has evolved and matured over the past decade, with several impending applications in various fields such as sensing, catalysis, and medicine. The exceptional feature of this technique is the formation of nanoparticles (colloids) and nanostructures (solids) in a single experiment with ultrashort laser pulses. We have been working on this technique for the past few years, investigating its potential using the surface-enhanced Raman scattering (SERS) technique in hazardous materials sensing applications. Ultrafast laser-ablated substrates (solids and colloids) could detect several analyte molecules at the trace levels/mixture form, including dyes, explosives, pesticides, and biomolecules. Here, we present some of the results achieved using the targets of Ag, Au, Ag-Au, and Si. We have optimized the nanostructures (NSs) and nanoparticles (NPs) obtained (in liquids and air) using different pulse durations, wavelengths, energies, pulse shapes, and writing geometries. Thus, various NSs and NPs were tested for their efficiency in sensing numerous analyte molecules using a simple, portable Raman spectrometer. This methodology, once optimized, paves the way for on-field sensing applications. We discuss the protocols in (a) synthesizing the NPs/NSs via laser ablation, (b) characterization of NPs/NSs, and (c) their utilization in the SERS-based sensing studies.

Introduction

Ultrafast laser ablation is a rapidly evolving field of laser-material interactions. High-intensity laser pulses with pulse durations in the femtosecond (fs) to picosecond (ps) range are used to generate precise material ablation. Compared to nanosecond (ns) laser pulses, ps laser pulses can ablate materials with higher precision and accuracy due to their shorter pulse duration. They can generate less collateral damage, debris, and contamination of the ablated material due to fewer thermal effects. However, ps lasers are typically more expensive than ns lasers and need specialized expertise for operation and maintenance. The ultrafast laser pulses enable precise contr....

Protocol

A typical protocol flowchart of the application of ultrafast ablated NPs or NSs in the trace detection of molecules via SERS is shown in Figure 1A.

1. Synthesizing metal NPs/NSs

NOTE: Depending on the requirement/application, choose the target material, the surrounding liquid, and the laser ablation parameters.
Here:
Target materials: Ag
Surrounding liquid: 10 mL of DI
Laser parameters: 35.......

Discussion

In ultrasonication cleaning, the material to be cleaned is immersed in a liquid and high-frequency sound waves are applied to the liquid using an ultrasonic cleaner. The sound waves cause the formation and implosion of tiny bubbles in the liquid, generating intense local energy and pressure that dislodge and remove dirt and other contaminants from the surface of the material. In laser ablation, a Brewster polarizer and a half-wave plate combination were used to tune the laser energy; the polarizer is typically placed bef.......

Materials

Name	Company	Catalog Number	Comments
Alloys	Local goldsmith	N/A	99% pure
Axicon	Thorlabs	N/A	100, IR range, AR coated, AX1210-B
Ethanol	Supelco, India	CAS No. 64-17-5
Femtosecond laser	femtosecond  (fs)  laser amplifier  Libra HE, Coherent	N/A	Pulse duraction 50 fs; wavelenngth 800 nm; Rep rate 1 KHz; Pulse Energy: 4 mJ
FESEM	Carl ZEISS, Ultra 55	N/A
Gatan DM3	www.gatan.com	Gatan Microscopy Suite 3.x
Gold target	Sigma-Aldrich, India		99% pure
HAuCl4.3H2O	Sigma-Aldrich, India	CAS No. 16961-25-4
High resolution translational stages	Newport SPECTRA PHYSICS GMBI	N/A	M-443 High-Performance Low-Profile Ball Bearing Linear Stage; The stage is only 1 inch high, and has 2 inches of travel.
Micro Raman	Horiba LabRAM	N/A	Grating-1,800 and 600 grooves/mm; Wavelength of excitation-785 nm,632 nm, 532 nm, 325 nm; Objectives 10x, 20x, 50 x, 100x; CCD detector
Mirrors	Edmund Optics	N/A	Suitable mirrors for specific wavelength of laser
Motion controller	NEWPORT SPECTRA PIYSICS GMBI	N/A	ESP300 Controller-3 axes control
Origin	www.originlab.com	Origin 2018
Picosecond laser	EKSPLA 2251	N/A	Pulse duraction 30ps; wavelenngth 1064 nm, 532 nm, 355 nm; Rep rate 10 Hz; Pulse Energy: 1.5 to 30 mJ
Planoconvex lens		N/A	focal length 10 cm
Raman portable	i-Raman plus,  B&W Tek, USA	N/A	785 nm, ~ 100 µm laser spot  fiber optic probe excitation and collection
Silicon wafer	Macwin India Ltd.		1–10 Ω-cm, p (100)-type
Silver salt (AgNO3)	Finar, India	CAS No. 7783-90-6
Silver target	Sigma-Aldrich, India	CAS NO 7440-22-4	99% pure
TEM	Tecnai TEM	N/A
TEM grids	Sigma-Aldrich, India	TEM-CF200CU	Copper Grid Carbon Coated  200 mesh
Thiram	Sigma-Aldrich, India	CAS No. 137-26-8
UV	Jasco V-670	N/A
XRD	Bruker D8 advance	N/A