We describe the preparation of a cotton swab for use in surface enhanced Raman scattering (SERS) by assembling silver nanoparticles (Ag-NPs) on common cotton. The flexibility of such cotton swabs allows for a close contact with sample surfaces by swabbing. This can considerably improve the sample collection efficiency. These cotton swabs exhibit excellent SERS activity as shown by the detection of rhodamine 6G at 0.81 pM concentration. The reproducibility of the intensity of SERS peaks is within 10 %. The applicability is demonstrated by in-situ detection of the fungicide carbaryl on a cucumber with an irregular surface. This combination of superior SERS activity, high reproducibility, accessibility in irregularly-shaped matrices and low-cost production indicates that such swabs offer a large potential in analytical SERS. Graphical Abstract A cost-effective surface enhanced Raman scattering (SERS) cotton swab is developed by assembling silver nanoparticles on common cotton. The SERS cotton swab can be used for in-situ sensitive detection of pesticide residue.