Gold nanoparticles are attractive as sensing materials because of their size and shape are related with their optical properties. The color change produced by the aggregation of functionalized AuNPs allows the detection of arsenic at low levels. A simple, cheap and fast analytical procedure to perform arsenic determination using functionalized gold nanoparticles (AuNPs) and VIS spectrometry as a detection technique is studied. Three different synthesis procedures to obtain the AuNPs and two different functionalization modes were studied. AuNPs functionalized with GSH-DTT-CYs-PDCA were selected as the most adequate. The correlation between the decrease in the absorbance signal and the arsenic concentration was good in the 2–20µgl−1interval. Repeatability, expressed as average of RSD (%), obtained for the different arsenic concentrations studied was 0.6%. The average value of the analytical recovery was 99.7%. The detection and quantifications limits were 2.5 and 8.4µgl−1 respectively. These limits are sufficient to detect World Health Organization’s guideline value of 10µgl−1. •Gold nanoparticles functionalized with GSH-DTT-CYs-PDCA for arsenic determination.•VIS Spectroscopy to determine arsenic in water at ppb levels.•Advantages of the method: simplicity, low cost, sensitivity, precision and time.