研究目的
To propose and demonstrate an optical discrimination technique for nanometric-sized, low optical absorbance molecular complexes adhering to thin metal films, using time-resolved evanescent-wave detection scheme in conjunction with hierarchical cluster analysis and principal value decomposition.
研究成果
The proposed optical discrimination technique, based on time-resolved evanescent-wave detection scheme in conjunction with hierarchical cluster analysis and principal value decomposition, successfully differentiates among molecular films based on statistical methods. This approach entails several advantages, including enhanced surface sensitivity and label-free molecular recognition. The technique has a high data throughput and can be integrated with existing microscopy platforms and lab-on-a chip architectures.
研究不足
The technique requires sophisticated equipment and data analysis methods. The sensitivity and specificity of the technique need to be further validated with a broader range of molecular complexes.
1：Experimental Design and Method Selection:
The experiment is based on a pump and probe optical scheme to investigate biomolecular layers with typical vertical dimensions of the order of less than 10 nm. The molecular layer is bound to an Au thin film deposited on the hypotenuse of a glass prism. A pump laser pulse excites the Au film. A time-delayed evanescent wave probe pulse, created at the glass-air interface of a prism in the Kretschmann configuration, probes a volume comprising the Au film and the molecular layers. The relative reflectivity variation of the probe pulse is recorded as a function of the time delay from the pump pulse arrival.
2：Sample Selection and Data Sources:
The experiments are performed on a BK7 prism hypotenuse, where a nominal thickness of 4 nm of gold is evaporated. The gold-coated prism is functionalized with a multifunctional copolymer of dimethylacrylamide (DMA), N-acryloyloxysuccinimide (NAS), and 3-(trimethoxysilyl) propyl methacrylate (MAPS)–copoly(DMA-NAS-MAPS)–providing reactive groups suitable for immobilizing molecular structures.
3：List of Experimental Equipment and Materials:
Pump and probe laser pulses are generated by two synchronized femtosecond fiber lasers with a repetition rate of 100 MHz and a pulse time width of 120 fs. The fundamental wavelength of 1560 nm of the first laser is used as a pump, while the second harmonic at 780 nm of the second laser is used as a probe. The delay between the pump and probe pulses is obtained by the Asynchronous Optical Sampling (ASOPS) technique.
4：Experimental Procedures and Operational Workflow:
The variation of the evanescent probe reflection induced by the optical pump has the ubiquitous decaying exponential shape. The dynamics measured on the different samples looks very similar, the signature of the specific time-response of individual molecular aggregates residing in tiny differences. Signal analysis methods are used to extract these differences and exploit them to discriminate among different molecular aggregates.
5：Data Analysis Methods:
The time-resolved spectra are analyzed using two approaches: a hierarchical binary cluster tree dendrogram built using a Euclidean distance (Ward method) and a singular value decomposition (SVD) analysis.
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