Detection of Molecules and Charges with a Bright Field Optical Microscope

Hao Zhu, Guangzhong Ma, Zijian Wan, Hui Wang, Nongjian Tao

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Charge is a fundamental property of a molecule, and precisely measuring it enables detection of the molecule and helps understand various chemical processes involving charge. Here we show a method to measure the charge of a single nanoparticle and binding of charged molecules to the nanoparticle using a conventional bright field optical microscope. The nanoparticle is tethered to an indium tin oxide surface with a polymer and driven into oscillation with an alternating electric field, which produces scattered light captured by a camera. The weak scattered light is separated from the intense bright field background using a Fourier transform filter, and the image contrast change provides the effective charge of the nanoparticle with precision of a few electron charges or less. This method allows us to detect DNA binding to the nanoparticles, demonstrating a simple method to detect and study molecules with a conventional optical microscope.

Original languageEnglish (US)
Pages (from-to)5904-5909
Number of pages6
JournalAnalytical Chemistry
Issue number8
StatePublished - Apr 21 2020

ASJC Scopus subject areas

  • Analytical Chemistry


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