Functionalized Gallium Nanoparticles for Enhanced Electrical Conductivity and Multifunctional Sensing Applications

Introduction:
Gallium (Ga) is a low-melting-point metal extensively used in soft electronics and sensors due to its thermal and electrical conductivity. However, during the synthesis of Ga nano-/microparticles, a passivating oxide layer often forms on the surface, which reduces conductivity. Traditional methods of oxide removal, such as mechanical sintering, lack control and may compromise the integrity of the system. Thus, there is a need for alternative approaches that prevent Ga oxidation while preserving electrical conductivity.
In this study, we introduce thiol-based molecules (1-butanethiol, thiophenol, and 4-mercaptopyridine) to functionalize Ga nano-/microparticles through sonication, which reduces surface oxidation and eliminates the need for a sintering step. We demonstrate that functionalizing Ga with these molecules enhances electrical conductivity via metal–molecule junctions, with 4-mercaptopyridine exhibiting the highest conductivity. Furthermore, these functionalized Ga particles are incorporated into soft devices, enabling gas, exhalation, and flex sensing capabilities. This study provides insights into using organic molecules to create electrically conductive Ga-based composites and offers prospects for advanced sensor applications.
Results:
We functionalized Ga nano-/microparticles by sonication with three different thiol molecules—1-butanethiol, thiophenol, and 4-mercaptopyridine—to prevent surface oxidation. Sonication facilitated the binding of these molecules to the Ga surface, forming metal–molecule junctions that eliminate the need for mechanical sintering. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) confirm a reduction in Ga oxide formation on the functionalized particles compared to untreated Ga particles.
Among the functionalized Ga systems, 4-mercaptopyridine-functionalized Ga exhibited superior electrical conductivity, which significantly outperforms the other thiolated Ga systems. This increase is attributed to the conjugation of organic molecules that provides continuous conductive pathways within the Ga matrix. Fourier-transform infrared (FTIR) spectroscopy confirmed the successful binding of 4-mercaptopyridine to the Ga surface.
We further integrated these functionalized Ga particles into soft devices, developing sensors capable of detecting gases, exhalation patterns, and flex movements. The high electrical conductivity of 4-mercaptopyridine-functionalized Ga enabled enhanced sensitivity and response times in these applications. Gas-sensing tests, particularly for carbon monoxide (CO), demonstrated a significant increase in responsivity compared to sensors using unmodified Ga particles. The flexibility of the composite material also made it suitable for wearable applications, where real-time monitoring of exhalation and movement was required.
Overall, this study introduces a novel method of functionalizing Ga nano-/microparticles with thiol-based molecules to prevent oxidation and enhance electrical conductivity without the need for sintering. The use of 4-mercaptopyridine was particularly effective, providing conductive pathways that improved sensor performance. The development of multifunctional sensors based on these particle systems highlights the potential for integrating organic molecules with liquid metal nanoparticles to create advanced materials for soft electronics and sensing applications. This work paves the way for future innovations in the design of liquid metal-based composites for a variety of technological applications.