PKmito ORANGE (also known under the name PKMO) is a bright, non-phototoxic & non-toxic mitochondrial probe based on the PKmito™ dyes developed by the lab of Zhixing Chen at Peking University1,2). PKmito ORANGE labels mitochondria in live cells with very high specificity. The unique and unmatched feature of PKmito ORANGE is its extremely low phototoxicity, due to the presence of the intramolecular triplet quencher cyclooctatetraene (COT) group. It allows to perform long term imaging of mitochondria without damaging them. PKmito ORANGE accumulates in the mitochondrial inner membrane (IM). It is highly suited to image mitochonridal cristae structure and dynamics by STED superresolution microscopy using a 775 nm depletion line. PKmito ORANGE does not require any genetic manipulation, transfection or overexpression of fluorescent proteins. PKmito ORANGE enables multicolor imaging with SPY505, SPY555, SPY620, SPY650, SPY700, SiR or GFP. It can be used for widefield, confocal, SIM or STED imaging in living cells and tissue. Contains 1 vial of PKmito ORANGE (lyophilized).

Absorbance maximum λabs

591 nm

Fluorescence maximum λfl

608 nm

Works on fixed cells?


Probe quantity

100 stainings*

Fluorescence lifetime

1.8 ns

STED depletion wavelength

775 nm


room temperature



Cells Stained with PKmito ORANGE

Cells Stained with PKmito ORANGE



Check out these videos of PKmito ORANGE in action

If you have any questions concerning this product, please contact our Technical Service department at

Q1. What is STED microscopy and how does it work?

A1. STED microscopy stands for Stimulated Emission Depletion microscopy.  It is one type of super resolution microscopy which allows the capture of images with a higher resolution than conventional light microscopy which is constrained by diffraction of light.  STED uses 2 laser pulses, one is the excitation pulse which excites the fluorophore, causing it to fluoresce.  The second pulse, referred to as the STED pulse, de-excites the fluorophore via stimulated emission in an area surrounding a central focal spot that is not de-excited and thus continues to fluoresce.  This is accomplished by focusing the STED pulse into a ring shape, a so-called donut, where the center focal spot is devoid of the STED laser pulse, conferring high resolution to the fluorescent area (Fig. 1; see Ref. 1 for more details on STED microscopy).


Figure 1. STED microscopic image of microtubules labeled with SiR-tubulin in human primary dermal fibroblasts.

Q2: Are the Spirochrome probes stable at room temperature?

A2: Yes, the probes are stable at room temperature for a few days.  However, it strongly depends on the probe and the solvent.  Thus, it is recommended to store all of the probes or solutions at –20°C.


1. Liu Tianyan et al. “Multi-color live-cell STED nanoscopy of mitochondria with a gentle inner membrane stain” PNAS (2022):119 (52).
2. Yang, Zhongtian, et al. “Cyclooctatetraene-conjugated cyanine mitochondrial probes minimize phototoxicity in fluorescence and nanoscopic imaging.” Chemical science 11.32 (2020): 8506-8516.