Pushing the resolution of infrared imaging by mid infrared photothermal microscopy

Fu, Pengcheng; Chen, Tianrun; Zhu, Hanlin; Xu, Chenran; Chen, Ming; Zhang, De‐Long

doi:10.1117/12.2575306

Cited by 2 publications

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“…IR imaging technology has expanded and diversified considerably in recent years with improvements in FT-IR imaging, [24][25][26] new designs to take advantage of synchrotron sources, [27][28][29][30][31] surfaceenhanced measurements utilizing plasmonic nanorod antennas, 32,33 QCL-based imaging instruments, [34][35][36][37][38][39][40][41][42][43] polarimetric imaging [44][45][46][47][48] and the emergence of hybrid techniques such as atomic force microscopy-IR imaging, 49,50 and photothermal microscopy. [51][52][53][54][55][56][57][58][59][60][61] Since many of these techniques are rapidly developing and their capabilities may not all be geared towards the chemical limit of detection, we focus this study largely on well-established FT-IR and QCL microscopes. These instruments still comprise a majority of those in use and provide representative examples of incoherent and coherent sources for new technologies to compare performance and improve upon.…”

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confidence: 99%

On the Limit of Detection in Infrared Spectroscopic Imaging

et al. 2021

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Infrared (IR) spectroscopic imaging instrumentsâ performance can be characterized and optimized by an analysis of their limit of detection (LoD). Here we report a systematic analysis of the LoD for Fourier transform IR (FT-IR) and discrete frequency IR (DFIR) imaging spectrometers. In addition to traditional measurements of sample and blank data, we propose a decision theory perspective to pose the determination of LoD as a binary classiï¬cation problem under different assumptions of noise uniformity and correlation. We also examine three spectral analysis approaches, namely absorbance at a single frequency, sum of absorbance over selected frequencies and total spectral distance â to suit instruments that acquire discrete or contiguous spectral bandwidths. The analysis is validated by reï¬ning the fabrication of a bovine serum albumin protein microarray to provide eight uniform spots from 2.8 nL of solution for each concentration over a wide range (0.05 -10 mg/mL). Using scanning parameters that are typical for each instrument, we estimate a LoD of 0.16 mg/mL and 0.12 mg/mL for wideï¬eld and line scanning FT-IR imaging systems, respectively, usingthespectraldistanceapproach,and0.22mg/mLand0.15mg/mL using an optimal set of discrete frequencies. As expected, averaging and the use of post-processing techniques such as minimum noise fraction (MNF) transformation results in LoDs as low as 0.075 mg/mL that correspond to a spotted protein mass of 112 fg/pixel. We emphasize that these measurements were conducted at typical imaging parameters for each instrument and can be improved using the usual trading rules of IR spectroscopy. This systematic analysis and methodology for determining the LoD can allow for quantitative measures of conï¬dence in imaging an analyteâs concentration and a basis for further improving IR imaging technology.

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