Chemical-Free MXene Nanoparticles Synthesized Using Femtosecond Bessel Beam for Flexible SERS Sensors

Flexible, versatile sensors prepared using simple, harsh chemical-free techniques are required for sensing hazardous molecules at low concentrations. In this work, we demonstrate a chemical-free, femtosecond laser-based synthesis procedure to achieve spherical Ti3C2 MXene nanoparticles via the technique of liquid-assisted laser ablation (LAL) while using a Bessel beam profile. The as-prepared MXene nanoparticles and their Au-decorated hybrids were deposited onto flexible filter paper substrates and evaluated as surface-enhanced Raman scattering (SERS) sensors for the trace-level detection of ammonium nitrate (AN), picric acid (PA), and Nile Blue (NB). The structural and compositional analyses (XRD, XPS, and TEM) confirmed near-complete etching of Al from Ti3AlC2 and successful incorporation of Au. The standalone MXene substrates provided a significant chemical enhancement [enhancement factor (EF)] of 103, enabling nanomolar detection of analytes without any noble metals. MXene/Au hybrids exhibited synergistic chemical and electromagnetic enhancements, achieving EF values of up to 105 for NB. These results highlight the potential of femtosecond laser-ablated MXene nanoparticles in filter paper as sustainable, flexible, and cost-effective SERS platforms for environmental and security sensing.