8th December 2020 | Analyst

Self-absorption corrected non-invasive transmission Raman spectroscopy (of biological tissue)

Benjamin Gardner, Pavel Matousek & Nicholas Stone


The first near infrared window in biological tissue (λ ∼ 700–950 nm) is of great interest for its potential to safely deliver light based diagnosis and therapeutic interventions, especially in the burgeoning field of nano-theranostics. In this context, Raman spectroscopy is increasingly being used to provide rapid non-invasive chemical molecular analysis, including bulk tissue analysis by exploiting the near infrared window, with transmission Raman spectroscopy (TRS). The disadvantage of this approach, is that when probing depths of several centimetres self-attenuation artefacts are typically exhibited, whereby TRS spectra can suffer from relative changes in the “spectral features” due to differential absorption of Raman photons by the various constituents of biological tissues. Simply put, for a homogenous substance with increasing thickness, spectral variances occur due to the optical properties of the material and not through changes in the chemical environment. This can lead to misinterpretation of data, or features of interest become obscured due to the unwanted variance. Here we demonstrate a method to correct TRS data for this effect, which estimates the pathlengths derived from peak attenuation and uses expected optical properties to transform the data. In a validation experiment, the method reduced total Raman spectral intensity variances >5 fold, and improved specific peak ratio distortions 35×. This is an important development for TRS, Spatially Offset Raman Spectroscopy (SORS) and related techniques operating at depth in the near IR window; applicable to samples where there is large sample thickness and inter- and intra-sample thickness is variable i.e. clinical specimens from surgical procedures such as breast cancer. This solution is expected to yield lower detection limits and larger depths in future applications such as non-invasive breast cancer diagnosis in vivo.

"A Window to the Depths"

— by Ryan Edginton —


Science Background

The near infra-red (NIR) optical windows are the wavelength ranges in which light penetrates deepest into the body. This is to say that our bodies are most transparent to red light a little beyond the visible spectrum. This is because the molecules that make up our tissues and life-fluids scatter and absorb less light at these wavelengths than for any other non-ionising radiation, so individual photons of NIR light can travel longer distances between molecules inside the body. Low powered NIR laser light can be used as a tool to see deep inside the body without piercing the skin or causing tissue damage.

A very small percentage of laser light experiences a slight, measurable wavelength change when scattered by a vibrating molecule; this is known as Raman scattering. Biological materials consist a collection of specific vibrating molecules that produce a distinct pattern of wavelength shifts unique to that biomaterial. This is like a chemical fingerprint and can be used to accurately identify the material.

A complication of measuring biological tissue deep inside the body in this way, is the myriad biomaterials contained in the intermediate space between internal target and external detector. These scatter and absorb the narrow spectrum of Raman scattered light by varied, wavelength-dependent amounts. The pattern of light wavelengths that reach the external detector, is therefore not the same as that measured directly at the target. This confuses the data and leads to possible misidentification of the internal biological tissue target.

Image Description

The artwork shows this wavelength-dependent variance in the transmission of Raman scattered light from-depth out of the body, resulting in non-chemical changes in the externally detected signal. The journal article describes a method developed to accurately correct for this effect.

In the background of the piece, a near infra-red laser beam is Raman scattered by a dense lump of cancer cells. 12 beams of light spread out from the tumour (6 red & 6 yellow; representing the spread of wavelength shifts contained in the scattered light), all travelling towards the foreground, passing through 3 stained-glass windows that differentially absorb the colour beams – 5 of the yellow beams reach you, the observer, but only 2 red beams successfully travel to this point.

The stained-glass windows are intended as a visual metaphor for the near infra-red optical window discussed above (hence the letters NIR on each pane). Choosing to layer the windows is representative of the depth and distance travelled by the Raman scattered light from the internal cancer to the surface of the skin, with increased absorbance potential at each stage.

The stained-glass contains depictions of light scattering (sunbeam pattern on the right), electronic and vibrational energy levels (concentric circles & enclosed triangles centred on the left), and the Raman spectra of lard, the sample studied in the journal article (undulating white line). The 880 cm-1 peak changes intensity whilst 1068 cm-1 remains fixed, reflecting the variable absorption of the Raman scattered wavelengths. Finally, overlapping golden orbs representing photons of light, fill the integral space beneath the spectra; the spectra being a count of the number of discrete Raman photons captured by the CCD camera detector.

22nd September 2020 | Analyst

Non-invasive Depth Determination of Inclusion in Biological Tissues using Spatially Offset Raman Spectroscopy with External Calibration

Sara Mosca, Priyanka Dey, Marzieh Salimi, Francesca Palombo, Nick Stone & Pavel Matousek


Spatially offset Raman spectroscopy (SORS) allows chemical characterisation of biological tissues at depths of up to two orders of magnitude greater than conventional Raman spectroscopy. In this study, we demonstrate the use of SORS for the non-invasive prediction of depth of an inclusion within turbid media (e.g. biological tissues) using only external calibration data sets, extending thus our previous approach that required internal calibration. As with the previous methodology, the concept is based on relative changes in Raman band intensities of the inclusion that are directly related to the path length of Raman photons travelling through the medium thereby encoding the information of depth of the inclusion. However, here the calibration model is created using data only from external measurements performed at the tissue surface. This new approach facilitates a fully non-invasive methodology applicable potentially to in vivo medical diagnosis without any a priori knowledge. Monte Carlo simulations of photon propagation have been used to provide insight into the relationship between the spatial offset and the photon path lengths inside the tissues enabling one to derive a general scaling factor permitting the use of spatial offset measurements for the depth prediction. The approach was validated by predicting the depth of surface-enhanced Raman scattering (SERS) labelled nanoparticles (NPs) acting as inclusions inside a slab of ex vivo porcine tissue yielding an average root mean square error of prediction of 7.3 % with respect to the overall tissue thickness. Our results pave the way for future non-invasive deep Raman spectroscopy in vivo by enabling, for example, the localisation of cancer lesions or cancer biomarkers in early disease diagnosis and targeted treatments.

14th July 2020 | Chemical Science

Diagnostic prospects and preclinical development of optical technologies using gold nanostructure contrast agents to boost endogenous tissue contrast

Priyanka Dey, Idriss Blakey & Nick Stone


Numerous developments in optical biomedical imaging research utilizing gold nanostructures as contrast agents have advanced beyond basic research towards demonstrating potential as diagnostic tools; some of which are translating into clinical applications. Recent advances in optics, lasers and detection instrumentation along with the extensive, yet developing, knowledge-base in tailoring the optical properties of gold nanostructures has significantly improved the prospect of near-infrared (NIR) optical detection technologies. Of particular interest are optical coherence tomography (OCT), photoacoustic imaging (PAI), multispectral optoacoustic tomography (MSOT), Raman spectroscopy (RS) and surface enhanced spatially offset Raman spectroscopy (SESORS), due to their respective advancements. Here we discuss recent technological developments, as well as provide a prediction of their potential to impact on clinical diagnostics. A brief summary of each techniques' capability to distinguish abnormal (disease sites) from normal tissues, using endogenous signals alone is presented. We then elaborate on the use of exogenous gold nanostructures as contrast agents providing enhanced performance in the above-mentioned techniques. Finally, we consider the potential of these approaches to further catalyse advances in pre-clinical and clinical optical diagnostic technologies.

"The Signaller"

— by Ryan Edginton —

The artwork features an antenna mast in the form of a human body – standing strong, arms raised skyward – with a cacophony of rainbow-coloured nanoparticle shapes creating the signal wave that broadcasts out across an open landscape.

The piece communicates how gold nanoparticles are helping to make non-invasive optical diagnostics a reality for future clinical practice. It specifically reflects the application of RaNT's surface enhanced spatially offset Raman spectroscopy (SESORS)-based technology.

The human body is the aerial from which the diagnostic signal radiates. A signal that is made strong enough to be detected non-invasively from outside of the body (without the aid of surgical probes), by inclusion of nanoparticles at potential disease sites deep within.

To symbolise this signal boosting power, the information waves being transmitted out of the body, dominating the surrounding landscape, are shown composed of all the nanoparticle shapes discussed in the paper (tentacles, rods, pyramids, prisms, stars, spheres, shells, rasberries, branches & chains).

In reality, the signals are a scattered spectrum of invisible (near infra-red; NIR) light wavelengths – represented by the rainbow colours – containing information on the type, location and size of potential tumour targets. This is all encoded in the relative intensities of specific wavelengths within the scattered light.

18th June 2020 | Advanced Science

Smart Gold Nanostructures for Light Mediated Cancer Theranostics: Combining Optical Diagnostics with Photothermal Therapy

Tanveer A. Tabish, Priyanka Dey, Sara Mosca, Marzieh Salimi, Francesca Palombo, Pavel Matousek & Nicholas Stone


Nanotheranostics, which combines optical multiplexed disease detection with therapeutic monitoring in a single modality, has the potential to propel the field of nanomedicine toward genuine personalized medicine. Currently employed mainstream modalities using gold nanoparticles (AuNPs) in diagnosis and treatment are limited by a lack of specificity and potential issues associated with systemic toxicity. Light‐mediated nanotheranostics offers a relatively non‐invasive alternative for cancer diagnosis and treatment by using AuNPs of specific shapes and sizes that absorb near infrared (NIR) light, inducing plasmon resonance for enhanced tumor detection and generating localized heat for tumor ablation. Over the last decade, significant progress has been made in the field of nanotheranostics, however the main biological and translational barriers to nanotheranostics leading to a new paradigm in anti‐cancer nanomedicine stem from the molecular complexities of cancer and an incomplete mechanistic understanding of utilization of Au‐NPs in living systems. This work provides a comprehensive overview on the biological, physical and translational barriers facing the development of nanotheranostics. It will also summarise the recent advances in engineering specific AuNPs, their unique characteristics and, importantly, tunability to achieve the desired optical/photothermal properties.

20th March 2020 | Journal of Raman Spectroscopy

Noninvasive simultaneous monitoring of pH and depth using surface‐enhanced deep Raman spectroscopy

Benjamin Gardner, Nicholas Stone & Pavel Matousek


Here we demonstrate the simultaneous recovery of multiplexed physical information of surface‐enhanced Raman scattering (SERS) nanoparticles (pH and depth) using deep Raman spectroscopy. As has been shown previously and in accordance with theory, inelastically scattered photons arising from spectral peaks that are suitably separated can exhibit different optical properties in the media through which they travel. These differences can impact the relative intensities of the Raman peaks as a function of the transmission path length; thereby, the depth of signal generation is inherently encoded in the spectra; assuming the target is clustered at a single depth or location, its depth can be readily determined. Moreover, Raman spectroscopy is very sensitive to chemistry of a sample, and changes in pH are observed not only as changes in peak intensity through relevant protonation and deprotonation but also as shifts in spectral features. Here, we show it is possible to precisely predict the depth (root‐mean‐square error [RMSE] 5 %) of SERS nanoparticles in scattering media (0.5% intralipid) while also being able to noninvasively monitor simultaneously the pH levels (RMSE ~0.2 pH units) of the media surrounding the nanoparticles. This is important as it demonstrates that nanoparticles can be used to report on multiple physical properties including their depth. This opens avenues for a range of new applications including the noninvasive diagnosis and localisation of cancer lesions in clinical environment in vivo.

28th February 2020 | Biomedical Optics Express

Optical characterization of porcine tissues from various organs in the 650–1100nm range using time-domain diffuse spectroscopy

Sara Mosca, Pranav Lanka, Nick Stone, Sanathana Konugolu Venkata Sekar, Pavel Matousek, Gianluca Valentini & Antonio Pifferi


We present a systematic characterization of the optical properties (µa and µs’) of nine representative ex vivo porcine tissues over a broadband spectrum (650-1100 nm). We applied time-resolved diffuse optical spectroscopy measurements for recovering the optical properties of porcine tissues depicting a realistic representation of the tissue heterogeneity and morphology likely to be found in different ex vivo tissues. The results demonstrate a large spectral and inter-tissue variation of optical properties. The data can be exploited for planning or simulating ex vivo experiments with various biophotonics techniques, or even to construct artificial structures mimicking specific pathologies exploiting the wide assortment in optical properties.

30th January 2020 | Small

Plasmonic Nanoassemblies: Tentacles Beat Satellites for Boosting Broadband NIR Plasmon Coupling Providing a Novel Candidate for SERS and Photothermal Therapy

Priyanka Dey, Tanveer A. Tabish, Sara Mosca, Francesca Palombo, Pavel Matousek & Nicholas Stone


Optical theranostic applications demand near‐infrared (NIR) localized surface plasmon resonance (LSPR) and maximized electric field at nanosurfaces and nanojunctions, aiding diagnosis via Raman or optoacoustic imaging, and photothermal‐based therapies. To this end, multiple permutations and combinations of plasmonic nanostructures and molecular “glues” or linkers are employed to obtain nanoassemblies, such as nanobranches and core–satellite morphologies. An advanced nanoassembly morphology comprising multiple linear tentacles anchored onto a spherical core is reported here. Importantly, this core‐multi‐tentacle‐nanoassembly (CMT) benefits from numerous plasmonic interactions between multiple 5 nm gold nanoparticles (NPs) forming each tentacle as well as tentacle to core (15 nm) coupling. This results in an intense LSPR across the “biological optical window” of 650−1100 nm. It is shown that the combined interactions are responsible for the broadband LSPR and the intense electric field, otherwise not achievable with core–satellite morphologies. Further the sub 80 nm CMTs boosted NIR‐surface‐enhanced Raman scattering (SERS), with detection of SERS labels at 47 × 10‐9 M, as well as lower toxicity to noncancerous cell lines (human fibroblast Wi38) than observed for cancerous cell lines (human breast cancer MCF7), presents itself as an attractive candidate for use as biomedical theranostics agents.