Photothermal spectroscopy and micro/nanofluidics

Abstract

Photothermal spectroscopy, a remarkable detection method that can analyze microscale objects in a noninvasive and nondestructive manner, has been successfully coupled with micro/nanofluidic devices. Specifically, methods that employ a thermal lens microscope (TLM), including a photothermal optical phase shift and photothermal optical diffraction, are a powerful tool for the sensitive detection of nonfluorescent or nonlabeled molecules in micro/nanofluidic channels. This review focuses on the family of TLMs in terms of their historical development. Their recent applications, ranging from separation, particle, biomedical, energy, and environmental analyses, are summarized, and future perspectives in nanoscale liquid science, system integration, and biological studies, such as single-cell analyses, are also discussed.

On-Chip Photonic Detection Techniques for Non-Invasive In Situ Characterizations at the Microfluidic Scale

“…When exposed to a focused laser beam, mostly in the infrared or near-infrared range, the absorbed energy is converted into heat by non-radiative relaxation following a profile corresponding to the beam’s focus. As liquids typically exhibit a negative temperature coefficient of the refractive index (d n /d T ), the central region of the excitation beam experiences a lower refractive index compared to the surrounding solution, inducing a concave lens effect, known as the thermal lens effect [ 137 ]. An excitation beam and a probe beam are focused in the same objective lens, so the small shift of the two laser focal points leads to the refraction of the probe beam due to the thermal lens effect ( Figure 7 ).…”

“…Sensors 2024, 24, x FOR PEER REVIEW 16 of 39 excitation beam experiences a lower refractive index compared to the surrounding solution, inducing a concave lens effect, known as the thermal lens effect [137]. An excitation beam and a probe beam are focused in the same objective lens, so the small shift of the two laser focal points leads to the refraction of the probe beam due to the thermal lens effect (Figure 7).…”

Photothermal Microscopy and Spectroscopy with Nanomechanical Resonators

“…The heterogeneity in size, shape, and composition of particles in samples further underscores the need to study absorption responses at the single-molecule and single-nanoparticle level. Advancements in so-called non-flourescence spectroscopy has enabled label-free detection, in most cases, and characterization of scarce concentrations of nanoparticles and molecules. − Specifically, developments in photothermal spectroscopy have facilitated the measurement of ever-lessening analyte concentrations as well as subdiffraction-limited localization of a large variety of single nanoparticles and molecules at room and cryogenic temperatures. As a result, photothermal spectroscopy has extended the scope of absorption spectroscopy, offering deeper insights into heterogeneous samples and finding applications in diverse fields like material science, catalysis, nanotechnology, and biophysics.…”

Thousand-Fold Enhancement of Photothermal Signals in Near-Critical CO2

“…Although most single-molecule studies are so far based on fluorescence, in the last few decades several fluorescence-free approaches , have been developed. Among them, photothermal (PT) microscopy − has shown strong promise. The sensitivity of PT microscopy enables the detection of the absorption of a single 1 nm gold nanoparticle (AuNP) and of single non-fluorescent molecules at room temperature.…”