Table 2.

Selected examples of SERS nanotags coatings.

Coating type	Comments	Reference
PEG	First example of successful in vivo tumor imaging using SERS nanotags covered by PEG layer attached directly to gold surface.	101
PEG, silica	While silica coating prevents Raman reporter from detaching from gold surface, PEG layer increases nanoparticles blood circulation time and decreases liver and spleen uptake.	12, 13, 26, 132
PDA	PDA coating not only granted SERS nanotags biocompatibility, but also allowed bone microfractures imaging due to high affinity of PDA towards calcium ions.	136
PMA-dodecylamine amide	Amphiphilic nature of the coating polymer allowed nanotags with high surface coverage by hydrophobic Raman reporters become hydrophilic and colloidally stable in water.	138
PEG, PMMA-co-4VP	Due to pH-sensitive nature of PMMA-co-4VP coating polymer, the multinanoparticle liposomal SERS construct could be disassembled in lysosomes following cellular uptake, allowing effective monitoring and controlled release of cargo.	140
Polyaniline Polypyrrole / PVP	Conjugated polymers for nanoparticles coating used in the study provided a viable alternative to organic dyes as SERS reporters, however they required additional coating with PVP to increase colloidal stability.	142
PNIPAm-co-AAm PEG	By coating drug-loaded branched gold nanoshells with thermoresponsive PNIPAm-co-AAm with a Raman reporter at a terminal end, it was possible to monitor photothermal heating and drug release from the nanoparticles by increase in SERS signal due to polymer collapse.	146
Polystyrene	Remarkably stable polystyrene coating for SERS nanotags allowed their storage for 6 months without significant loss of SERS intensity.	147
Silica	First primer-free silica coating protocol that allowed to achieve unprecedentedly high SERS intensities due to absence of competition for surface for the Raman reporter.	26
Silica	Ultrasound-assisted silica coating of nanoparticles can increase the shell stability towards hydrolysis.	160
BSA	BSA coating was shown to better protect gold nanostars from reshaping into spheres and aggregation than PEG coating after storage for 24 hours at room temperature.	104
DNA	Coating SERS nanotags with oligonucleotides was demonstrated to not only increase the particles colloidal stability, but also allowed simultaneous imaging and quantification of multiple miRNAs inside cells in vitro.	170
Lipids	Lipid membrane coating of gold nanoparticles allows encapsulation of multitude of different Raman reporters inside it, removing the requirements for Raman reporters to have anchoring groups or charges.	173