What do we actually see in intracellular SERS? Investigating nanosensor-induced variation

Abstract

Plasmonic nanoparticles (NPs), predominantly gold (AuNPs), are easily internalised into cells and commonly emloyed as nanosensors for reporter-based and reporter-free intracellular SERS applications 1 . While AuNPs are generally considered non-toxic to cells, many biological and toxicity studies report that exposure to NPs induces cell stress through generation of reactive oxygen species (ROS) and upregulated transcription of pro-inflammatory genes, which can result in severe genotoxicity and apoptosis 2 . Despite this, the extent to which normal cellular metabolism is affected by AuNP internalisation remains a relative unknown along with the contribution of the uptake itself to the SERS spectra obtained from within so called 'healthy' cells, as indicated by traditional viability tests. This work aims to interrogate the perturbation created by treatment with AuNPs under different conditions and the corresponding effect on the SERS spectra obtained. We characterise the changes induced by varying AuNP concentrations and media-serum compositions using biochemical assays and correlate them to the corresponding intracellular reporter-free SERS spectra. The different serum conditions lead to different extents of nanoparticle internalisation. We observe that changes in SERS spectra are correlated to increasing amount of internalisation, confirmed qualitatively and quantitatively by confocal imaging and ICP-MS analysis, respectively. We analyse spectra and characterise changes that can be attributed to nanoparticle induced changes. Thus, our study points to the need to understand condition-dependent NP-cell interactions and standardisation of nanoparticle treatments to establish the validity of intracellular SERS experiments and for use of the methodology for all arising applications.

Surface-Enhanced Raman Scattering for Label-Free Living Single Cell Analysis

“…The use of gold nanoparticles (AuNPs) without any targeting moieties by Mahajan’s group was also reported to be useful in cellular monitoring studies taking advantage of particle uptake and they could detect cell differentiation upon drug stimulation . Several other approaches were applied to deliver SERS substrates into cells by various research groups, preferentially AuNPs for their less cytotoxic behavior compared to silver nanoparticles (AgNPs), by both endosomal uptake or intracellular AuNP growth as well as through mechanical approaches such as electroporation or microinjection. − The approach utilized by Mahajan’s group, where label- and targeting moiety-free SERS is used, has started to gain attention for its ease of implementation and alternative cellular condition monitoring. , …”

“…Although it is not straightforward to answer this question, a plausible hypothesis can be devised by focusing on the journey of substrates into living cells from cell culture medium. Because the observed spectra originate from a few nanometers of away from the NP surface into the surrounding medium, molecular environment on the NP surface should be taken into consideration in the light of current knowledge. − …”

“…45−47 The approach utilized by Mahajan's group, where label-and targeting moietyfree SERS is used, has started to gain attention for its ease of implementation and alternative cellular condition monitoring. 48,49 ■ LABEL-FREE LIVING SINGLE CELL SERS Utilizing label-and targeting moiety-free SERS in any biological applications brings out one ultimate question to the mind before data interpretation that is "What is the origin of observed spectral bands?". Although it is not straightforward to answer this question, a plausible hypothesis can be devised by focusing on the journey of substrates into living cells from cell culture medium.…”

Tracing Size and Surface Chemistry-Dependent Endosomal Uptake of Gold Nanoparticles Using Surface-Enhanced Raman Scattering

“…This was due to the different adsorptions of biomolecules on different composite nanostructures. In another study, Mahajan’s group demonstrated that even though it was not visible on the cell viability results, the increased uptake could perturb the intracellular functions . As seen, these parameters play an important role in cellular functions, spectral outcome, and SERS signal quality.…”

Detection of mycoplasma in contaminated mammalian cell culture using FTIR microspectroscopy

“…IR spectral differences have been reported on many biological samples from cancerous and normal cells, cells in different growth stages or different environments, studying the effect of drugs on cells, and plant cells [ 7 – 20 ] to bacterial and parasite identification [ 19 , 21 – 23 ] and so on. Parallel techniques such as SERS (surface-enhanced Raman scattering) were also used to evaluate nanomaterials cytotoxicity on living cells and the changes they induced [ 24 , 25 ].…”