DAPI (hydrochloride) (Synonyms: 4',6Diamidino2phenylindole, FxCycle Violet)

DAPI, as a DNA-specific probe, can form a fluorescent complex by attaching in the minor grove of A-T rich sequences of DNA and nonfluorescent intercalative complexes with double-stranded nucleic acids. DAPI, as a chromosome and nuclear stain, has maximum excitation ultraviolet (UV) light wavelength with 358 nm and emission in the blue range with 461 nm.^[1]

DAPI is usually used for flow cytometry, chromosome staining, DNA visualization and quantitation in histochemistry and biochemistry.^[2] DAPI is a good substrate of hOCT1 with a Michaelis constant of 8.94 µM.^[6].

In vitro, DAPI (1.43µM) can measure mitochondrial permeability transition and mitochondrial membrane depolarization by combining with Annexin V(FITC)and the potentiometric fluorescent dye, tetramethylrhodamine methyl ester (TMRM).^[3] In vitro, to evaluate the DAPI fluorescence, SSC buffer (pH 7.2), containing 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04% SDS or Triton X-100 and 2 µg/mL of DAPI dye, there was found that a linear relationship between DAPI fluorescence and Triton X-100 concentrations ranging from 0.01 to 0.04%.^[4] In addition, when the concentration of DAPI was increased from 0.4 μM to 400 μM, the total signal intensity increased, implying an increase in the concentration of DAPI molecules bound to the chromosomes.^[5] In vitro experiment it shown that treatment with NR 1 μg/mL, DAPI 5 μg/mL, ORO 0.3% (v/v) and CV 0.5% (v/v) provided optimal linearity and coverage of signals over a range of cell densities (corresponding to 10-100% cell confluence).^[7].

References:
[1] Karg TJ, et al. Photoconversion of DAPI and Hoechst dyes to green and red-emitting forms after exposure to UV excitation. Chromosoma. 2018 Jun;127(2):235-245.
[2] Kapuscinski J. DAPI: a DNA-specific fluorescent probe. Biotech Histochem. 1995 Sep;70(5):220-33.
[3] Wallberg F, et al. Analysis of Apoptosis and Necroptosis by Fluorescence-Activated Cell Sorting. Cold Spring Harb Protoc. 2016 Apr 1;2016(4):pdb.prot087387.
[4] Šimoliūnas E, et al. DNA-DAPI Interaction-Based Method for Cell Proliferation Rate Evaluation in 3D Structures. Curr Issues Mol Biol. 2021 May 30;43(1):251-263.
[5] Estandarte AK, et al. The use of DAPI fluorescence lifetime imaging for investigating chromatin condensation in human chromosomes. Sci Rep. 2016 Aug 16;6:31417.
[6] Yasujima T, et al. Characterization of human OCT1-mediated transport of DAPI as a fluorescent probe substrate. J Pharm Sci. 2011 Sep;100(9):4006-12.
[7] Phan MAT, et al. Semi-quantification of lipids in human meibomian gland epithelial cells using dual staining microplate assays. Exp Eye Res. 2021 Sep;210:108719.