# Recent Developments in Plasmonic Sensors of Phenol and Its Derivatives
## 5 Plasmonic Resonance-Based Raman Sensors for Detection of Phenolic Compounds
### Hybrid Nanomaterial-Based Raman Sensors  
As one of the most efficient plasmonic materials, hybrid nanomaterials--either bimetallic nanostructures or nanocomposites--have been widely adapted to prepare Raman substrates used in various fields as biosensors and environments. Recently, a novel Raman method has been developed to detect phenolic acids--vanillic acid, syringe acid, and gallic acid--using three-dimensional nanoprobes of a self-assembled composite of GNPs and SiO\({}_{2}\)[34]. In addition, AgNP-embedded poly (diallyl dimethyl-ammonium) chloride has been successfully used as a Raman substrate for biosensors, where this substrate was fabricated by modifying graphene oxide nanosheets. AgNPs have been well designed, yielding highly dense hotspots for enhanced Raman signals [105]. Owing to their excellent electromagnetic mechanism, bimetallic nanostructures have been used predominantly as biosensors, as shown in Figure 9.  
Figure 8: (**A**) Schematic diagram of Raman detection of dopamine (DA) using DNA-assisted synthesis of ortho-nanodimers (DaSON) of AgNPs. SEM images of Raman platforms with a scale bar of 500 nm (**B**) before and (**C**) after the adsorption of Raman probes containing DA aptamers and DTNB. Inserted pictures show an enlarged view of the yellow rectangle. Adapted from [104].  
Some authors have successfully self-assembled core-shell structured dimers of bimetallic Au@Ag nanorods, which were used as Raman nanosensors, particularly for detecting dopamine--a neurotransmitters--playing a key role in life. Based on aptamers and the electronic field of Ag shell coating outside the Au nanorod dimer, Raman signals have been well enhanced, indicating that the substrates exhibited an ultra-sensitive limit of dopamine detection at 0.006 PM [11]. As shown in Figure 10, Raman detection of chloropheds was investigated by MIPs based on composites of SiO2, FGO, and Au. Nanocomposite-based Raman have significantly enhanced signals, leading high sensitivity in chlorophend detection [106]. Despite numerous efforts of Raman sensors based on plasmonic materials as nanostructures of noble metals and hybrids, more scientific studies are required to develop functional plasmonic nanostructured materials used for optical sensors. To understand plasmonic phenomena and interfaces of materials, some authors have discovered various MOF structures and revealed their effective ability for multi-detection of phenolic substances using SERS spectroscopy. In the next section, this review reveals several significant contributions to phenolic compound detection from MOF-assisted SERS sensors, according to some interesting examples.  
Figure 10: (**A**) Schematic diagram of trace detection of 2,6-DCP using Raman spectroscopy and MIPs based on nanocomposites of SiO2 /rGO/Au. (**B**) TEM images of (a) SiO2 /rGO, (b) composites of 12,6-DCP, (c) composites of 12,6-DCP, (d) composites of 12,6-DCP, (e) composites of 12,6-DCP, (f) composites of 12,6-DCP, (f) composites of 12,6-DCP, (g) composites of 12,6-DCP, (h) composites of 12,6-DCP, (h) composites of  
of polydopamine modified SiO2/rGO/Au, (c) nanocomposites of SiO2/rGO/Au, and (d) SEM image of SiO2/rGO/Au nanocomposites. (**C**) Concentration-dependent Raman spectra of 2,6-DCP. (**D**) Linear curve of 2,6-DCP concentration-correlated Raman intensities at 661 cm1. Adapted from [106].