Mid-IR Fluorescence Photothermal Microscopy for Component Separation

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Solution Overview

Problem

Existing photothermal infrared microscopy methods struggle with mechanical speed limits and the inability to distinguish between materials with similar IR signatures, particularly in turbid and heterogeneous pharmaceutical samples, due to weak temperature-dependent refractive index changes and complex optical interactions.

Innovation Solution

A fluorescence-detected mid-infrared photothermal microscopy system using a multichannel laser array modulates infrared beams to generate fluorescence responses, applying optical binary masks and non-negative matrix factorization for rapid discrimination between sample components with similar IR signatures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If photothermal AFM-IR is used to achieve nm-scale spatial resolution, then measurement precision is improved, but productivity deteriorates due to mechanical response time limits requiring several minutes for a single image

Engineering Contradiction:

Improvespatial resolutionVSAvoidimaging speed

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent replaces the mechanical cantilever detection system with an optical detection system. Instead of using the mechanical response of an AFM cantilever to detect photothermal signals, the invention uses optical methods (such as interferometry or photothermal lensing) to detect temperature changes induced by IR absorption. This substitution eliminates the mechanical response time bottleneck while maintaining nm-scale spatial resolution through optical focusing capabilities.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Productivity

If O-PTIR is used to overcome mechanical speed limits, then productivity is improved, but measurement precision deteriorates due to weak refractive index temperature dependence and complex optical interactions in turbid samples

Engineering Contradiction:

Improveimaging speedVSAvoidsignal detection accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent changes the detection parameter from refractive index (which has weak temperature dependence of about 0.01% per°C) to direct temperature measurement using optical methods. By detecting the photothermal lens effect or using interferometric techniques that directly measure temperature-induced optical path length changes, the system achieves higher sensitivity to temperature changes, improving signal detection accuracy in turbid pharmaceutical samples.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If conventional O-PTIR is used for transmission measurements, then measurement precision is improved for homogeneous media, but device complexity increases and adaptability deteriorates for turbid and heterogeneous pharmaceutical samples

Engineering Contradiction:

Improvespectral assignment accuracyVSAvoidsample type compatibility

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent develops a detection system that can handle multiple sample types (homogeneous media, turbid samples, powdered materials, opaque solids) using a unified optical detection approach. The system incorporates detection geometries and signal processing methods that are adaptable to various sample configurations, making the photothermal microscopy technique universally applicable to pharmaceutical materials analysis without requiring separate optimized systems for each sample type.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The system provides μm-scale spatial resolution and improved discrimination between materials with similar IR characteristics, enhancing signal-to-noise ratio through temperature-dependent fluorescence changes, enabling accurate identification of components in turbid and heterogeneous samples.

Implementation Method 1

energizing a sample with one or more modulated infrared (IR) beams... whereby the multichannel laser output is modulated thereby modulating the heating at a predetermined frequency

Methodology Applied

Scientific EffectPhotothermal heating: Absorption (EM radiation)

Implementation Method 2

concurrently continuously illuminating the sample with a probe beam, thereby generating a fluorescence response signal... thereby modulating the fluorescence response signal

Methodology Applied

Scientific EffectFluorescence: Fluorescence

Data Source

PatentUS12449363B2Fluorescence-detected mid-infrared photothermal microscopy

Publication Date: 2025.10.21 PURDUE RES FOUND

AI summary

A method of selectively photothermally heating a sample in a fluorescence-detected mid-infrared photothermal microscopy is disclosed which includes energizing a sample with one or more modulated infrared (IR) beams sourced by a multichannel laser array, concurrently continuously illuminating the sample with a probe beam, thereby generating a fluorescence response signal, capturing the fluorescence response signal, processing the captured modulated fluorescence response signal into two IR absorption spectra corresponding to chemical properties of two components in the sample by scanning over each channel of the multichannel laser array, generating a binary mask associated with the two spectra, establishing a cost function based on the generated binary mask, optimizing the cost function by optimizing the binary mask, and selectively energizing channels of the multichannel laser array based on the optimized binary mask thereby maximizing discrimination between the two components.