Label-free single-substrate quantitative protein assay based on optical characteristics of cholesteric liquid crystals

Mon Juan Lee*, Chao Ping Pai, Po Chang Wu, Wei Lee

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Cholesteric liquid crystal (CLC) is characterized by the selective reflection in the Bragg condition for constructive interference. Instead of assembling a LC cell with a pair of glass substrates, only a single glass substrate modified with vertical alignment reagent and layered with a CLC film of 3.4 ± 0.2 μm in thickness was utilized in this study for the detection of bovine serum albumin (BSA). By fine-tuning the ratio of the thickness d to the helical pitch P of the CLC film, both qualitative and quantitative biosensing capabilities were demonstrated with an E7/R811 CLC (d/P close to but smaller than unity) and an E7/R5011 CLC (d/P > > 1) film, respectively. The E7/R811 film was in the unwound homeotropic state in the absence of BSA, but transitioned to the fingerprint state at 10−9 to 10−6-g/ml BSA and to the planar state between 10−5 and 10−2-g/ml BSA. Quantitative protein assay based on E7/R5011 CLCs was established through transmission spectrometric analysis, and detection sensitivity was optimized by adjusting the Bragg reflection wavelength. A limit of detection of 5.9 × 10−9 g/ml was achieved for the CLC film consisting of 2.0-wt% R5011 in the nematic host E7 and exhibiting a Bragg reflection wavelength of 700 nm. As a majority of clinical assays are performed on a single solid substrate, the CLC-based, single-substrate biosensing platform allows for better integration with current technologies. Besides, the protein array employed in this work can be further miniaturized and converted to a protein microarray format to facilitate high-throughput analysis.

Original languageEnglish
Article number115756
JournalJournal of Molecular Liquids
StatePublished - 1 Jun 2021


  • Bovine serum albumin
  • Cholesteric liquid crystal
  • Label-free biosensor
  • Optical biosensor
  • Protein assay
  • Transmission spectrometry

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