Table 1 Comparison between the different advanced spatial phenotyping techniques for vibrational spectroscopic imaging

From: Spatial analysis of the osteoarthritis microenvironment: techniques, insights, and applications

Imaging technique

Representative technique

Working Principle

Spatial Resolution

Advantages

Disadvantages

Metabolite detected

Application in OA

Vibrational spectroscopic imaging

NIR

Reflect C-H, N-H, and O-H stretching and bending overtones from 12 500 to 4 000 cm−1

100 μm172

Fast, accurate, nondestructive, labor-saving

Wideband, high spectral overlap, challenging to distinguish characteristic peak, hard to distinguish exact mass

GAG, PG173

High penetration but only full spectral signal of cartilage

MIR/FTIR

Reflects molecular vibrational and rotational energy level transitions (4 000-400 cm−1)

10 μm174

Fast, accurate, and nondestructive; reflects the information of most organic matter

Low signal on bone, challenging to distinguish characteristic peak, hard to distinguish exact mass

PG,48 type II collagen,50 CS623

Detects a multitude of components in the cartilage and can perform high-speed imaging

Nano MIR/FTIR

Combining FTIR with s-SNOM. Based on AFM, an external light source illuminates a sharp tip, and the tip-scattered light (usually backscattered) is measured as a function of tip position

Up to 20 nm42

Fast, accurate, and nondestructive; reflects the information of most organic matter

Low signal on bone, difficult to distinguish characteristic peak, hard to distinguish exact mass

N/A

Detects a multitude of components in the cartilage, can perform high-speed imaging, and can detect subcellular changes

Raman spectroscopy

Reflects the vibrational information between molecules based on the principle of Raman scattering

1 μm–250 nm51

Weak water signal, fast and straightforward, reflects the biological signal

The optical system and fluorescence interference can alter the Raman scattering region.

V2PO43-, V4PO43-, V1PO43-, V3 PO43-, V1CO32-, Hydroxyproline, Amide I, Amide III, Saturated lipids, Unsaturated lipids, CH2 twist, GAG, PG, β(CH2) lipids, CH lipids, CH2 wag, β (CH2/ CH3) lipids, Tryptophan, Phenylalanine, Proline, Phenylalanine, Tyrosine51

Reflects physiological changes of OA and can reach subcellular level

  1. NIR Near-infrared spectroscopy, GAG Glycosaminoglycan, PG Proteoglycan, CS6 chondroitin 6-sulfate, Nano MIR/FTIR Nanoscale mid-infrared/Fourier transform infrared spectroscopy, s-SNOM Scattering-type scanning near-field optical microscopy, AFM Atomic force microscopy, N/A Not applicable
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