KeywordsArsenic (As3+)ColorimetricSurface-enhanced Raman spectroscopy (SERS)Gold nanoparticles (AuNPs)1. IntroductionArsenic (As3+) contamination in drinking water has attracted considerable attention [1]. The highly As3+ intake would increase the risks of cancer in the skin, lungs, bladder, diabetes and kidney diseases [2]. The arsenic levels in groundwater recommend by the World Health Organization (WHO) is less than 10 ppb [3]. Up to now, different detection techniques for As3+ have been developed, including atomic fluorescence spectrometry (AFS) [4], atomic absorption spectroscopy (AAS) [5], electrochemical method [6], mass spectrometry (MS) [7], and fluorimetry [8]. However, these methods are associated with the shortcoming of lengthy protocols, complex steps, and costly instrumentation [9]. Hence, it is still imperative for development of simple, rapid and sensitive methods to detect As3+ ion.In recent decades, the colorimetric based on functionalized metal nanoparticles has been the mainstay for detection of As3+ due to its simplicity, visualization and low-cost [10], including lauryl sulfate functionalized AuNPs [11], ranolazine functionalized copper nanoparticles [12], polyethylene glycol functionalized AuNPs [13], and PEG functionalized silver nanoparticles [14], and so on. However, the colorimetric detection is easy to be interfered by the colors of samples and the detection limit of colorimetric is sometimes not satisfied [15].To compensate for the shortcomings of colorimetric, a dual-mode sensing system combining colorimetric and surface-enhanced Raman scattering (SERS) have been constructed [16], [17], [18], [19], which has several distinct advantages. First, SERS can provide a fingerprint signal of analyses, which supports the achievement of an unprecedented detection limitation [20], [21], [22]. Second, the combination of colorimetric and SERS into one detection system can ensure highly efficacious and sensitive screening of numerous samples [23,24]. Third, a dual-mode sensing system can provide more than one output signal at the same time, making the detection results more convincing [25,26].In our assays, we proposed a strategy for colorimetric/SERS dual-mode sensing of As3+ based on glutathione functionalized gold nanoparticles (GSH/AuNPs). The presence of As3+ could induce aggregation of AuNPs, giving rise to wine red-to-blue color change. Meanwhile, the aggregated AuNPs could provide abundant hot spots to serve as an excellent substrate for SERS detection with the help of R6G probe. This dual-mode sensing system combines the advantages of both colorimetric and SERS methods, which would have practical potential application for rapid detection of As3+.