In this research paper, we study the Fano resonance originating from the interaction of in-phased lattice collective resonance and anti-phased lattice collective resonance supported by a binary silicon nanodisk array. Experimental results agree well with the calculations using finite-difference-time-domain method and show a strong dependence of such Fano lineshapes on the radius difference of the particles in the array. Further calculations demonstrate that such binary silicon nanodisk array can be used as an optical filter and offers an efficient way to tune the linewidth simply by changing the radius of the particles, linewidth from 12 nm to 0.7 nm and corresponding Q factor from 72 to 1290 as the radius R(2) increasing from 60 nm to 115 nm. Such scheme possessing the merits of being easily fabricated, simulated, and tuned is very promising for practical applications.

Colorectal cancer is the second leading cause of cancer death in the United States. Significant limitations in screening and surveillance modalities continue to hamper early detection of primary cancers or recurrences after therapy. In this study, we describe a new registered ultrasound (US) and acoustic-resolution photoacoustic microscopy (AR-PAM) system and report its initial testing in ex vivo human colorectal tissue. A total of 8 colorectal specimens were imaged, which included 2 polyps, 4 malignant colon cancers, and 2 treated colorectal cancers. In each specimen, normal tissue was also imaged for internal control. Initial data have demonstrated the feasibility of identifying colorectal cancer imaging features and the invasion depth using co-registered US and an AR-PAM system. In normal tissue, we found that our system consistently demonstrates the multi-layer structure of normal colonic tissue while differentiating layers with elevated vascularity; these findings highly correlated with histologic findings of each specimen. For malignant colorectal samples, the tissue structure is highly disorganized as seen in US, and photoacoustic imaging revealed distorted vascular distribution inside the tumor. Notably, AR-PAM of tumor beds after complete tumor destruction by radiation and chemotherapy yielded a pattern identical to benign tissue. Quantitative analysis of photoacoustic spectral slope has demonstrated more high-frequency components in malignant tissue as compared to the normal colon tissue, which may be caused by significantly increased microvessel networks. In summary, we demonstrate the successful differentiation of benign and malignant colorectal tissue with our co-registered ultrasound and photoacoustic system.

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