Nanosecond-resolution photothermal dynamic imaging via MHZ digitization and match filtering

AbstractPhotothermal microscopy has enabled highly sensitive label-free imaging of absorbers, from metallic nanoparticles to chemical bonds. Photothermal signals are conventionally detected via modulation of excitation beam and demodulation of probe beam using lock-in amplifier. While convenient, the wealth of thermal dynamics is not revealed. Here, we present a lock-in free, mid-infrared photothermal dynamic imaging (PDI) system by MHz digitization and match filtering at harmonics of modulation frequency. Thermal-dynamic information is acquired at nanosecond resolution within single pulse excitation. Our method not only increases the imaging speed by two orders of magnitude but also obtains four-fold enhancement of signal-to-noise ratio over lock-in counterpart, enabling high-throughput metabolism analysis at single-cell level. Moreover, by harnessing the thermal decay difference between water and biomolecules, water background is effectively separated in mid-infrared PDI of living cells. This ability to nondestructively probe chemically specific photothermal dynamics offers a valuable tool to characterize biological and material specimens.

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Nanosecond-Resolution Photothermal Dynamic Imaging via MHz Digitization and Match Filtering

10.21203/rs.3.rs-496390/v1 ◽

2021 ◽

Author(s):

Jiaze Yin ◽

Lu Lan ◽

Yi Zhang ◽

Hongli Ni ◽

Yuying Tan ◽

...

Keyword(s):

Metallic Nanoparticles ◽

Modulation Frequency ◽

Single Pulse ◽

Dynamic Imaging ◽

Pulse Excitation ◽

Label Free ◽

Mid Infrared ◽

Excitation Beam ◽

Match Filtering ◽

Lock In

Abstract Photothermal microscopy has enabled highly sensitive label-free imaging of absorbers, from metallic nanoparticles to chemical bonds. Photothermal signals are conventionally detected via modulation of excitation beam and demodulation of probe beam using lock-in amplifier. While convenient, the wealth of thermal dynamic is not revealed. Here, we present a lock-in free, mid-infrared photothermal dynamic imaging (PDI) system by MHz digitization and match filtering at harmonics of modulation frequency. Thermal-dynamic information is acquired at nanosecond resolution within single pulse excitation. Our method not only increases the imaging speed by two orders of magnitude, but also obtains four-fold enhancement of signal-to-noise ratio over lock-in counterpart, enabling high-throughput metabolism analysis at single-cell level. Moreover, by harnessing the thermal decay difference between water and biomolecules, water background is effectively separated in mid-infrared PDI of living cells. This ability to nondestructively probe chemically specific photothermal dynamics offers a valuable tool to characterize biological and material specimens.

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expansion with a heterodyne laser interferometer (laser probe). Demodulation is obtained with specific electronics. The magnitude and phase of the surface vibration are given with a second lock-in amplifier (lock-in amplifier 1) and stored in a microcomputer that also drives the scanning units. With this multi-acquisition microscope, the typical duration of an experiment in order to obtain a set of five low noise images is about 15 minutes. The resolution of the SThEM is given by the size at the photothermal source (radius of the optical beam: 5 /xm here). 4.1. Application to the study of thin films The first example concerns the observation of subsurface thin layers. In order to demonstrate the capacity for subsurface investigation we successively vapour deposited a 200 nm thick SiC>2 and 100 nm thick aluminium layers onto a polycrystalline nickel substrate (Fig. 8a). The bright strip on the right part of the image (Fig. 8b) reveals the presence of the subsurface SiC>2 layer which is optically invisible. This image has been obtained at 220 kHz modulation frequency of the excitation beam. The image contrast corresponds to about 25° phase shift. As the SThEM makes it possible to observe the subsurface we decided to use it for the detection of thin films delamination. We used a 1 /xm thick DLC film deposited on a steel substrate. Several lines of Vickers indentations were performed under an applied load of 4.5N. A different spacing (25 to 140 pim) between indentations has been taken for each line. The SEM and thermoelastic images of the indentations spaced 25 /xm are shown in Fig. 9. Due to the film delamination, an optically invisible bright area between the indentations (Fig. 9a) was observed by the SThEM at 100 kHz operating frequency (Fig. 9b). It is an indication of the excessive heating resulting from the film delamination. The latter is due to the tensile residual stresses which develop around each indentation. The bright area (film delamination) could not be detected both in the case of a single indentation or when the spacing between indentations was higher than 40 /xm. In the latter case

Adhesion Aspects of Thin Films, Volume 1 ◽

10.1201/b11971-32 ◽

2014 ◽

pp. 210-212

Keyword(s):

Thin Films ◽

Steel Substrate ◽

Modulation Frequency ◽

Low Noise ◽

Nickel Substrate ◽

Polycrystalline Nickel ◽

Excitation Beam ◽

The Right ◽

Lock In ◽

Bright Area

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Graphene-Based Biosensors for Detection of Composite Vibrational Fingerprints in the Mid-Infrared Region

Nanomaterials ◽

10.3390/nano9101496 ◽

2019 ◽

Vol 9 (10) ◽

pp. 1496

Author(s):

Yijun Cai ◽

Yanfen Hang ◽

Yuanguo Zhou ◽

Jinfeng Zhu ◽

Jingwen Yang ◽

...

Keyword(s):

Limit Of Detection ◽

Graphene Nanoribbons ◽

Infrared Region ◽

Infrared Range ◽

Label Free ◽

Mid Infrared ◽

Performance Limit ◽

Wide Range ◽

Vibrational Signals ◽

Physical Insight

In this study, a label-free multi-resonant graphene-based biosensor with periodic graphene nanoribbons is proposed for detection of composite vibrational fingerprints in the mid-infrared range. The multiple vibrational signals of biomolecules are simultaneously enhanced and detected by different resonances in the transmission spectrum. Each of the transmission dips can be independently tuned by altering the gating voltage applied on the corresponding graphene nanoribbon. Geometric parameters are investigated and optimized to obtain excellent sensing performance. Limit of detection is also evaluated in an approximation way. Besides, the biosensor can operate in a wide range of incident angles. Electric field intensity distributions are depicted to reveal the physical insight. Moreover, another biosensor based on periodic graphene nanodisks is further proposed, whose performance is insensitive to the polarization of incidence. Our research may have a potential for designing graphene-based biosensor used in many promising bioanalytical and pharmaceutical applications.

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