Large-Scale Flexible Surface-Enhanced Raman Scattering (SERS) Sensors with High Stability and Signal Homogeneity

Abstract

Flexible surface-enhanced Raman scattering (SERS) sensors have attracted great attention as a portable and low-cost device for chemical and bio-detection. However, flexible SERS sensors tend to suffer low signal spatial homogeneity due to the uneven distribution of active plasmonic nanostructures (hot spots) and quick degradation of their sensitivity due to low adhesion of hot spots and flexible substrates during fast sampling. Herein, a large-area (20 × 20 cm 2 ) polyimide (PI)-based SERS sensor is exploited for trace detection with high signal homogeneity and stability. The SERS sensor is constructed from PI through in situ growth of silver and gold core−shell nanoparticles (Ag@Au NPs) based on chemical reduction and galvanic replacement processes. Benefiting from the abundant carboxyl groups on the surfacecleaved PI, densely and uniformly distributed Ag@Au NPs are successfully prepared on the film under ambient conditions. The high Raman enhancement factor (EF) (up to 1.07 × 10 7 ) and detection capability with low nanomolar (10 −9 M) detection limits are obtained for this flexible SERS sensor. The uniform Raman signals in the random region show good signal homogeneity with a low variation of 8.7%. Moreover, the flexible SERS sensor exhibited superior efficiency and durability after storage for 30 days even after 500 cycles of mechanical stimuli (bending or torsion). The residue of pesticide thiram (tetramethylthiuram disulfide, TMTD) has been rapidly traced by direct sampling from the apple surface, and a sensitivity of 10 ng/cm 2 for TMTD was achieved. These findings show that the PI-based SERS sensor is a very strong candidate for broad and simple utilization of flexible SERS for both laboratory and commercial applications in chemical and biomolecule detections.

Towards practical and sustainable SERS: a review of recent developments in the construction of multifunctional enhancing substrates

“…This method typically involves in-situ chemical reduction of noble metal precursors physically dispersed in a flexible and adsorptive matrix, such as paper or textile. [109][110][111][112] For example, Ge, et al reported a large-scale synthesis of flexible cotton SERS wipes for trace analysis of surface residues. 113 The cotton SERS wipes were produced by dipping cotton sheets in AgNO 3 solution and then in a solution of ascorbic acid reducing agent, which led to the formation of Ag nanoparticles on the surface of the cotton fibers.…”

“…swab dry sample for ex-situ analysis 0.13 ng (ClO4 -), 0.13 ng (ClO3 -) and 0.11 ng (NO3 -) on aluminum foil Ag@Au NPs polyimide film [110] in-situ growth 8.7% (30 points on one substrate)…”

Au@Ag Dendritic Nanoforests for Surface-Enhanced Raman Scattering Sensing

“…SERS measurements typically utilize the induced surface plasmons on a metal surface to chemically or physically enhance the intensity of Raman scattering [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. SERS is an ultrasensitive vibrational spectroscopic technique used to detect molecules near the surface of plasmonic nanostructures.…”

“…Using SERS of individual Ag colloidal NPs can achieve optical detection and spectroscopy of single molecules and NPs at room temperature [ 2 ]. Flexible SERS sensors were achieved through the fabrication of Ag–Au core-shell NPs based on chemical reduction and Galvanic replacement processes on a polyimide (PI) substrate [ 9 ].…”

“…Au–Ag NPs also have benefits in terms of chemical stability for long-term use. The flexible SERS sensor consisted of Ag and Au core-shell NPs on a PI substrate exhibited superior efficiency and durability after storage for 30 days and even after 500 cycles of mechanical stimuli (bending or torsion) [ 9 ]. Ag-based hybrid nanoprobes have shown their tremendous potential for SERS imaging of precise biological detection and mediated phototherapy [ 32 ].…”