Bottom-up assembled photonic crystals for label-free sensing: Evaluation between photonic band gap and Fabry-Perot fringes

The major challenge of the application of photonic crystals (PhCs) biosensors is the test sensitivity, selectivity, and reliability of the target analytes in complex real samples, like bodily fluids. Herein, we introduce the concept of utilizing the optical thickness (OT), which came from Fabry Perot fringes (F-P fringes), of bottom-up assembled PhCs to replace the traditional photonic band gap (PBG) as a parameter for biosensing process monitoring and quantification of analytes. The bottom-up assembled silica PhCs films are specialized to own a thickness with good interferometric properties and an ordered porous interconnecting and mechanically stable structure as a scaffold for biological reactions. By selecting a specific diameter (190 nm) of the silica PhCs building block, both PBG and F-P fringes can be observed on the spectrum simultaneously at the range of white light, and during detection, mutual interference between the two can be minimized to a great extent. This study finds that nearly 14 times lower low limit of detection (LLoD) can be achieved with F P fringes than the PBG in ethanol concentration benchmark test on the same silica PhCs film. The thrombolysis experiment and human immunoglobulin G content evaluation in human plasma also show the sensitivity and reliability of F P fringes in real samples, which PBG property can not perform well. This is the first systematic comparison study on PBG and F P fringes in silica PhCs films.

Automated summary

The major challenge in the application of photonic crystal biosensors is to improve the sensitivity, selectivity, and reliability of detecting target analytes in complex real samples. This study introduces the concept of utilizing the optical thickness of bottom-up assembled photonic crystals as a parameter for biosensing, and finds that it shows higher sensitivity and reliability compared to the traditional photonic band gap parameter in real samples.