Assessment of spatially offset Raman spectroscopy to detect differences in bone matrix quality

Since spatially offset Raman spectroscopy (SORS) can acquire biochemical measurements of tissue quality through light scattering materials, we investigated the feasibility of this technique to acquire Raman bands related to the fracture resistance of bone. Designed to maximize signals at different offsets, a SORS probe was used to acquire spectra from cadaveric bone with and without skin-like tissue phantoms attenuating the light. Autoclaving the lateral side of femur mid-shafts from 5 female and 5 male donors at 100 °C and again at 120 °C reduced the yield stress of cortical beams subjected to three-point bending. It did not affect the volumetric bone mineral density or porosity. Without tissue phantoms, autoclaving affected more Raman characteristics of the organic matrix when determined by peak intensity ratios, but fewer matrix properties depended on the three offsets (5 mm, 6 mm, and 7 mm) when determined by band area ratios. The cut-off in the thickness of the tissue phantom layers was ∼4 mm for most properties, irrespective of offset. Matching trends when spectra were acquired without phantom layers between bone and the probe, ν1PO43-/Amide III and ν1PO43-/(proline + OH-proline) were higher and lower in the non-treated bone than in the autoclaved bone, respectively, when the thickness of tissue phantom layers was 4 mm. The layers, however, caused a loss of sensitivity to autoclaving-related changes in ν3CO3/ν1PO43- and crystallinity. Without advanced post-processing of Raman spectra, SORS acquisition through turbid layers can detect changes in Raman properties of bone that accompany a loss in bone strength.

Sensitivity of the amide I band to matrix manipulation in bone: a Raman micro-spectroscopy and spatially offset Raman spectroscopy study

The fracture resistance of bone arises from the hierarchical arrangement of minerals, collagen fibrils (i.e., cross-linked triple helices of α1 and α2 collagen I chains), non-collagenous proteins, and water. Raman spectroscopy (RS) is not only sensitive to the relative fractions of these constituents, but also to the secondary structure of bone proteins. To assess the ability of RS to detect differences in the protein structure, we quantified the effect of sequentially autoclaving (AC) human cortical bone at 100 °C (∼34.47 kPa) and then at 120 °C (∼117.21 kPa) on the amide I band using a commercial Raman micro-spectroscopy (μRS) instrument and custom spatially offset RS (SORS) instrument in which rings of collection fiber optics are offset from the central excitation fiber optics within a hand-held, cylindrical probe. Being clinically viable, measurements by SORS involved collecting Raman spectra of cadaveric femur mid-shafts (5 male & 5 female donors) through layers of a tissue mimic. Otherwise, μRS and SORS measurements were acquired directly from each bone. AC-related changes in the helical status of collagen I were assessed using amide I sub-peak ratios (intensity, I, at ∼1670 cm-1 relative to intensities at ∼1610 cm-1 and ∼1640 cm-1). The autoclaving manipulation significantly decreased the selected amide I sub-peak ratios as well as shifted peaks at ∼1605 cm-1 (μRS), ∼1636 cm-1 (SORS) and ∼1667 cm-1 in both μRS and SORS. Compared to μRS, SORS detected more significant differences in the amide I sub-peak ratios when the fiber optic probe was directly applied to bone. SORS also detected AC-related decreases in I1670/I1610 and I1670/I1640 when spectra were acquired through layers of the tissue mimic with a thickness ≤2 mm by the 7 mm offset ring, but not with the 5 mm or 6 mm offset ring. Overall, the SORS instrument was more sensitive than the conventional μRS instrument to pressure- and temperature-related changes in the organic matrix that affect the fracture resistance of bone, but SORS analysis of the amide I band is limited to an overlying thickness layer of 2 mm.

Shining Light on Osteoarthritis: Spatially Offset Raman Spectroscopy as a Window into Cartilage Health

Articular cartilage is a complex tissue, and early detection of osteoarthritis (OA) is crucial for effective treatment. However, current imaging modalities lack molecular specificity and primarily detect late-stage changes. In this study, we propose the use of Spatially Offset Raman Spectroscopy (SORS) for non-invasive, depth-dependent, and molecular-specific diagnostics of articular cartilage. We demonstrate the potential of SORS to penetrate deep layers of cartilage, providing a comprehensive understanding of disease progression. Our SORS measurements were characterized and validated through mechanical and histological techniques, revealing strong correlations between spectroscopic measurements and both Young's modulus and depth of cartilage damage. By longitudinally monitoring enzymatically degraded condyles, we further developed a depth-dependent damage-tracking method. Our analysis revealed distinct components related to sample depth and glycosaminoglycan (GAG) changes, offering a comprehensive picture of cartilage health. Collectively, these findings highlight the potential of SORS as a valuable tool for enhancing OA management and improving patient outcomes.

Raman spectroscopy in skeletal tissue disorders and tissue engineering: present and prospective

Musculoskeletal disorders are the most common reason of chronic pain and disability representing worldwide an enormous socio-economic burden. In this review, new biomedical application fields for Raman spectroscopy (RS) technique related to skeletal tissues are discussed showing that it can provide a comprehensive profile of tissue composition in situ, in a rapid, label-free, and non-destructive manner. RS can be used as a tool to study tissue alterations associated to aging, pathologies, and disease treatments. The main advantage with respect to currently applied methods in clinics is its ability to provide specific information on molecular composition, which goes beyond other diagnostic tools. Being compatible with water, RS can be performed without pre-treatment on unfixed, hydrated tissue samples, without any labelling and chemical fixation used in histochemical methods. This review provides first the description of basic principles of RS as a biotechnology tool and introduces into the field of currently available RS based techniques, developed to enhance Raman signal. The main spectral processing statistical tools, fingerprint identification and available databases are mentioned. The recent literature has been analysed for such applications of RS as tendon and ligaments, cartilage, bone, and tissue engineered constructs for regenerative medicine. Several cases of proof-of-concept preclinical studies have been described. Finally, advantages, limitations, future perspectives, and challenges for translation of RS into clinical practice have been also discussed.

A New Frontier for Nondestructive Spatial Analysis of Pharmaceutical Solid Dosage Forms: Spatially Offset Low-Frequency Raman Spectroscopy

A new Raman subtechnique, spatially offset low-frequency Raman spectroscopy (SOLFRS), is demonstrated via an analysis of pharmaceutical solid dosage forms. Several different model systems comprised of celecoxib (a popular anti-inflammatory drug), α-lactose anhydrous stable form, α-lactose monohydrate, and polyvinylpyrrolidone (PVP) were used to represent tangible scenarios for the application of SOLFRS. Additionally, the challenges and limitations were highlighted in relation to its real-time use, and potential solutions to address them were also provided. Lastly, the future directions for this new variation of Raman spectroscopic technique were briefly discussed, including its potential for broader application in pharmaceutical analysis and other research fields.

Spatially offset Raman spectroscopy for biomedical applications

In recent years, Raman spectroscopy has undergone major advancements in its ability to probe deeply through turbid media such as biological tissues. This progress has been facilitated by the advent of a range of specialist techniques based around spatially offset Raman spectroscopy (SORS) to enable non-invasive probing of living tissue through depths of up to 5 cm. This represents an improvement in depth penetration of up to two orders of magnitude compared to what can be achieved with conventional Raman methods. In combination with the inherently high molecular specificity of Raman spectroscopy, this has therefore opened up entirely new prospects for a range of new analytical applications across multiple fields including medical diagnosis and disease monitoring. This article discusses SORS and related variants of deep Raman spectroscopy such as transmission Raman spectroscopy (TRS), micro-SORS and surface enhanced spatially offset Raman spectroscopy (SESORS), and reviews the progress made in this field during the past 5 years including advances in non-invasive cancer diagnosis, monitoring of neurotransmitters, and assessment of bone disease.

Investigating the feasibility of spatially offset Raman spectroscopy for in-vivo monitoring of bone healing in rat calvarial defect models

A wide range of biomaterials and tissue-engineered scaffolds are being investigated to support and stimulate bone healing in animal models. Using phantoms and rat cadavers, we investigated the feasibility of using spatially offset Raman spectroscopy (SORS) to monitor changes in collagen concentration at levels similar to those expected to occur in vivo during bone regeneration (0-0.84 g/cm³ ). A partial least squares (PLS) regression model was developed to quantify collagen concentration in plugs consisting of mixtures or collagen and hydroxyapatite (predictive power of ±0.16 g/cm³ ). The PLS model was then applied on SORS spectra acquired from rat cadavers after implanting the collagen: hydroxyapatite plugs in drilled skull defects. The PLS model successfully predicting the profile of collagen concentration, but with an increased predictive error of ±0.30 g/cm³ . These results demonstrate the potential of SORS to quantify collagen concentrations, in the range relevant to those occurring during new bone formation.

Determination of inclusion depth in ex vivo animal tissues using surface enhanced deep Raman spectroscopy

This work presents recent developments in spatially offset and transmission Raman spectroscopy for noninvasive detection and depth prediction of a single SERS inclusion located deep inside ex vivo biological tissues. The concept exploits the differential attenuation of Raman bands brought about by their different absorption due to tissue constituents enabling to predict the inclusion depth. Four different calibration models are tested and evaluated to predict the depth of surface enhanced Raman scattering labelled nanoparticles, within an up to 40 mm slab of porcine tissue. An external measurement carried out in transmission mode, with a noninvasively built model on the analysed sample, is shown to be insensitive to variations of the overall thickness of the tissue yielding an average root-mean-square error of prediction of 6.7%. The results pave the way for future noninvasive deep Raman spectroscopy in vivo enabling to localise cancer biomarkers for an early diagnosis of multiple diseases.

Rapid Discrimination of Malaria- and Dengue-Infected Patients Sera Using Raman Spectroscopy

Malaria and dengue have overlapping clinical symptoms and are prevalent in the same geographic region (tropical and subtropical), hence precise diagnosis is challenging. The high mortality rate associated with both malaria and dengue could be attributed to "false", "delayed", or "missed" diagnosis. The present study thus aims to stratify malaria and dengue using Raman spectroscopy (RS). In total, 130 human sera were analyzed for model development and double-blinded testing. Principal components linear discriminant analysis (PC-LDA) of acquired RS-spectra could classify malaria and dengue with a minor overlap of 16.7%. Receiver operating characteristic (ROC) analysis of test samples showed sensitivity/specificity of 0.9529 for malaria vs healthy controls (HC) and 0.9584 for dengue vs HC. The Raman findings were complemented by mass spectroscopy (MS)-based metabolite analysis of 8 individuals, each from malaria, dengue, and HC. Several of the metabolites, including amino acids, cell-free DNA, creatinine, and bilirubin, assigned for the predominant RS-bands were also identified by MS and showed similar trends. Our data clearly indicates that RS-based serum analysis using a microprobe has immense potential for early, accurate, and automated detection and discrimination of malaria and dengue, and in the future, it could be extrapolated in field-settings combined with hand-held RS. Further, this approach might be extended to diagnose other closely related infections with similar clinical manifestations.

Heat-induced Bone Diagenesis Probed by Vibrational Spectroscopy

Complementary vibrational spectroscopic techniques - infrared, Raman and inelastic neutron scattering (INS) - were applied to the study of human bone burned under controlled conditions (400 to 1000 °C). This is an innovative way of tackling bone diagenesis upon burning, aiming at a quantitative evaluation of heat-induced dimensional changes allowing a reliable estimation of pre-burning skeletal dimensions. INS results allowed the concomitant observation of the hydroxyl libration (OHlibration), hydroxyl stretching (ν(OH)) and (OHlibration + ν(OH)) combination modes, leading to an unambiguous assignment of these INS features to bioapatite and confirming hydroxylation of bone's inorganic matrix. The OHlib, ν(OH) and ν4(PO43-) bands were identified as spectral biomarkers, which displayed clear quantitative relationships with temperature revealing heat-induced changes in bone's H-bonding pattern during the burning process. These results will enable the routine use of FTIR-ATR (Fourier Transform Infrared-Attenuated Total Reflectance) for the analysis of burned skeletal remains, which will be of the utmost significance in forensic, bioanthropological and archaeological contexts.

Spatially offset Raman spectroscopy for in vivo bone strength prediction

Bone strength is a worldwide health concern. Although multiple techniques have been developed to evaluate bone quality, there are still gaps to be filled. Here we report a non-invasive approach for the prediction of bone strength in vivo using spatially offset Raman spectroscopy. Raman spectra were acquired transcutaneously from the tibiae of mice from 4 to 23 weeks old and subsequently on the exposed bones. Partial least squares regression was applied to generate predictions of the areal bone mineral density (aBMD), volumetric bone mineralization density (vBMD), and maximum torque (MT) of each tibia as quantified by dual-energy X-ray absorptiometry, microCT imaging, and biomechanical tests, respectively. Significant correlations were observed between Raman spectral predictions and the reference values in all three categories. To our knowledge, this is the first demonstration of Raman spectroscopy predicting a biomechanical bone parameter (MT) in vivo with an uncertainty much smaller than the spread in the reference values.

Multiplex imaging of live breast cancer tumour models through tissue using handheld surface enhanced spatially offset resonance Raman spectroscopy (SESORRS)

Through utilizing the depth penetration capabilities of SESORS, multiplexed imaging and classification of three singleplex nanotags and a triplex of nanotags within breast cancer tumour models is reported for the first time through depths of 10 mm using a handheld SORS instrument.

In-vivo Raman spectroscopy: from basics to applications

For more than two decades, Raman spectroscopy has found widespread use in biological and medical applications. The instrumentation and the statistical evaluation procedures have matured, enabling the lengthy transition from ex-vivo demonstration to in-vivo examinations. This transition goes hand-in-hand with many technological developments and tightly bound requirements for a successful implementation in a clinical environment, which are often difficult to assess for novice scientists in the field. This review outlines the required instrumentation and instrumentation parameters, designs, and developments of fiber optic probes for the in-vivo applications in a clinical setting. It aims at providing an overview of contemporary technology and clinical trials and attempts to identify future developments necessary to bring the emerging technology to the clinical end users. A comprehensive overview of in-vivo applications of fiber optic Raman probes to characterize different tissue and disease types is also given.

Through tissue imaging of a live breast cancer tumour model using handheld surface enhanced spatially offset resonance Raman spectroscopy (SESORRS)

Detection of a live 3D tumour model through 15 mm of tissue using SESORRS.

In order to improve patient survival and reduce the amount of unnecessary and traumatic biopsies, non-invasive detection of cancerous tumours is of imperative and urgent need. Multicellular tumour spheroids (MTS) can be used as an ex vivo cancer tumour model, to model in vivo nanoparticle (NP) uptake by the enhanced permeability and retention (EPR) effect. Surface enhanced spatially offset Raman spectroscopy (SESORS) combines both surface enhanced Raman spectroscopy (SERS) and spatially offset Raman spectroscopy (SORS) to yield enhanced Raman signals at much greater sub-surface levels. By utilizing a reporter that has an electronic transition in resonance with the laser frequency, surface enhanced resonance Raman scattering (SERRS) yields even greater enhancement in Raman signal. Using a handheld SORS spectrometer with back scattering optics, we demonstrate the detection of live breast cancer 3D MTS containing SERRS active NPs through 15 mm of porcine tissue. False color 2D heat intensity maps were used to determine tumour model location. In addition, we demonstrate the tracking of SERRS-active NPs through porcine tissue to depths of up to 25 mm. This unprecedented performance is due to the use of red-shifted chalcogenpyrylium-based Raman reporters to demonstrate the novel technique of surface enhanced spatially offset resonance Raman spectroscopy (SESORRS) for the first time. Our results demonstrate a significant step forward in the ability to detect vibrational fingerprints from a tumour model at depth through tissue. Such an approach offers significant promise for the translation of NPs into clinical applications for non-invasive disease diagnostics based on this new chemical principle of measurement.

Towards establishing a minimal nanoparticle concentration for applications involving surface enhanced spatially offset resonance Raman spectroscopy (SESORRS) in vivo

Detection of SERRS nanotags at picomolar concentrations through 5 mm of tissue using SESORS.