A near-infrared Nile red fluorescent probe for the discrimination of biothiols by dual-channel response and its bioimaging applications in living cells and animals

Abstract

Biothiols, including cysteine (Cys), homocysteine (Hcy), glutathione (GSH) and H₂S, play important roles in human physiological processes. However, it is a great difficulty to distinguish biothiols from each other because of their similar chemical properties. Based on Nile red, we have designed and synthesized a near-infrared fluorescent probe for discriminating Cys/Hcy from GSH/H₂S by a dual-channel detection method. Using an ether bond, near-infrared Nile red was attached to 7-nitrobenzofurazan to construct the probe. Due to the photo-induced electron transfer, the probe showed almost no fluorescence from the green to red emission band. But upon the addition of Cys (0-150 μM) or Hcy (0-200 μM), the probe exhibited a noteworthy fluorescence "turn-on" signal in two unique emission bands (Green and Red) with a fast response (within 30 min). In contrast, the probe displayed an increase in fluorescence only in the red channel when encountering GSH (0-70 μM) or H₂S (0-50 μM), and GSH/H₂S could be tested respectively by different response time. The limit of detection was calculated to be 0.09 μM (Cys), 0.30 μM (Hcy), 0.24 μM (GSH), and 0.04 μM (H₂S), respectively (based on S/N = 3). The desirable dual-channel detection could be achieved in serum samples and living cells. Moreover, the probe could be applied for bioimaging in mice, which indicated its potential application in the clinic.