With the world population predicted to reach 9.8 billion by 2050, it is necessary to increase food production accordingly. Unfortunately, crops are under a number of threats from insects, diseases or competing weeds. Thus, pesticides are widely used to protect crops and increase yield at the same time. Amongst these, 2,4-dichlorophenoxyacetic acid (2,4-D, C8H6Cl2O3) is a phenoxy herbicide that is extensively applied in agriculture to control weeds in corn and grain field. Unfortunately, there is growing evidence that 2,4-D is harmful both to human health and the environment. To prevent or minimize negative impacts from the use of pesticides, the European Union has regulated their use and has provided strict guidelines for their application. For example, a maximum residue limits (MRL) of 0.1 ppb (parts per billion) for individual pesticide has been established. However, despite these precautions, pesticides can still leach from the ground into water and run off in nearby water bodies. 2,4-D in particular has good solubility in water and traces above the MRL have been found in river and drinking water. To this end, it is necessary to monitor 2,4-D pesticides and possibly prevent pollution events. The most common method currently used to detect 2,4-D in real environment is by applying chromatography to purify the small molecule, followed by mass spectrometry (HLC-MS) to qualitatively identify the herbicides. Unfortunately, this method is time-consuming and requires high-end equipment operated by skilled personnel in dedicated laboratories. To tackle this challenge, numerous of methods have been investigated in recent years for simpler 2,4-D detection, including platforms based on electrochemistry, fluorescence, 10 chemiluminescence, etc. Amongst them, optical detection based on surface enhanced Raman spectroscopy (SERS) has shown tremendous potential. Surface Enhanced Raman Spectroscopy is mostly based on the enhanced Raman signal by metallic nano structures that can generate strong electromagnetic field with the excitation at certain laser wavelength. SERS is an ultra-sensitive technology that is capable of providing a spectral fingerprint of the analytes under investigation. The magnitude of the SERS enhancement depends on the morphology, the size of the metallic nano particles, the gap size between the metallic nano particles, the measurement environment, as well as the wavelength of the laser excitation source. Because of the simplicity of operation and sensitivity in detection, SERS has been used for trace detection of 2,4-D pesticides including: SERS substrates based on hollow Au@Ag nano-snowflake particles functionalized with 4-MBA/2,4-D antigen, citrate functionalized AgNPs on cellulose paper, silver NPs with molecular imprint polymers (MIP), highly roughened surface flower-like Ag NPs. Particularly, SERS substrates based on well-ordered AuNPs inside mesostructured silica channels have been used to detect 2,4-D, with the limit of detection (LOD) down to 0.79 ppt (parts per trillion) achieved. These methods require either (i) an incubation time of more than 1 h, (ii) a pre-treatment step by mixing the solution with ethanol, or (iii) waiting time to allow 2,4-D solution to dry on the SERS substrate. To rapid determine pesticides such as 2,4-D directly in water samples without any pretreatment remains a key challenge.