Rapid real-time monitoring of NO released from living cells using multi-walled carbon nanotube-7,7,8,8-tetracyanoquinonedimethyl-polylysine sensors

Nitric oxide (NO) is an important but short-lived signaling molecule that is released from living cells. Real-time monitoring of NO release is useful for understanding normal cellular physiology and pathology. Herein, a convenient and efficient NO sensor was developed using multiwalled carbon nanotubes (MWCNTs)-7,7,8,8-tetracyanoquinodimethan (TCNQ)-polylysine (PLL) modified screen-printed electrode (SPE). The construction of the sensor (MWCNTs/TCNQ/PLL/SPE) was based on the synergic effect of the good conductivity of TCNQ and the high surface area of MWCNTs. The introduction of the cell-adhesive molecule PLL significantly enhanced the cytocompatibility, resulting in excellent cell attachment and growth. The resulting MWCNTs/TCNQ/PLL/SPE was successfully used for the real-time detection of NO released from living human umbilical vein endothelial cells (HUVECs) cultured on it. The MWCNTs/TCNQ/PLL/SPE was further used to detect NO release from oxidative-injured HUVECs with and without resveratrol to also preliminarily assess the effect of resveratrol against oxidative damage. The sensor developed in this study showed good performance for the real-time detection of NO released by HUVECs under different conditions and has potential applications in the diagnosis of biological processes and the screening of drug treatment effects.

A ratiometric near-infrared fluorescence/photoacoustic dual-modal probe with strong donor dithienopyrrole for in vivo nitric oxide detection

Integrating the imaging techniques of near-infrared fluorescence (NIRF) and photoacoustic (PA) can make up for each other and provide more useful medical information. Ratiometric imaging activated by disease-associated biomarkers can further augment imaging specificity. However, very few studies have employed the NIRF/PA dual-modal ratiometric imaging to improve the accuracy and specificity of disease diagnosis to date. In this paper, we present the synthesis of a nitric oxide (NO)-activated ratiometric NIRF/PA dual-modal nanoprobe RAPNP for in vivo NO imaging. The ratiometric imaging function was achieved jointly by a NO/acidity-responsive molecule DTP-BTDA and a nonresponsive fluorophore DTP-BBTD. In these fluorophores, the dithienopyrrole (DTP) moiety had strong electron-donating ability and imparted strong intramolecular charge transfer and relatively long emission wavelengths. The BTDA moiety in DTP-BTDA could be rapidly oxidized by NO under weak acidic environments, achieving the NIRF and PA signal activation. By using RAPNP as a contrast agent, we achieved the ratiometric detection of the endogenous NO in inflammatory bowel disease by NIRF/PA dual-modal imaging. This work provides the first case of the NIRF/PA dual-signal ratiometric probe for the real-time detection of NO in vivo.

A highly photostable and versatile two-photon fluorescent probe for the detection of a wide range of intracellular nitric oxide concentrations in macrophages and endothelial cells

Nitric oxide (NO) is involved in many biological processes affecting the cardiovascular, nervous and immune systems. Intracellular NO can be monitored using fluorescent probes in combination with fluorescence imaging techniques. Most of the currently available NO fluorescent molecular probes are excited via one-photon excitation using UV or Vis light, which results in poor penetration and high photodamage to living tissues. Here, we report a two-photon fluorescent molecular probe, DANPY-NO, able to detect NO in live cells. The probe consists of an o-phenylenediamine linked to a naphthalimide core; and operates via photoinduced electron transfer. DANPY-NO exhibits good sensitivity (LOD of 77.8 nM) and high selectivity towards NO, and is stable over a broad range of pHs. The probe targeted acidic organelles within macrophages and endothelial cells, and demonstrated enhanced photostability over a commercially available NO probe. DANPY-NO was used to selectively detect endogenous NO in RAW264.7ϒ NO^- macrophages, THP-1 human leukemic cells, primary mouse (bone marrow-derived) macrophages and endothelial cells. The probe was also able to detect exogenous NO in endothelial cells and distinguish between increasing concentrations of NO. The NO detection was evidenced using confocal laser scanning and two-photon microscopies, and flow cytometry. Further evidence was obtained by recording the changes in the intracellular fluorescence emission spectrum of the probe. Importantly, the probe displayed negligible toxicity to the analysed biological samples. The excellent sensitivity, selectivity, stability and versatility of DANPY-NO confirm its potential for in vitro and in vivo imaging of NO.

CuO/Cu-MOF nanocomposite for highly sensitive detection of nitric oxide released from living cells using an electrochemical microfluidic device

The integration of large surface area and high catalytic profiles of Cu-MOF and CuO nanoparticles is described toward electrochemical sensing of nitric oxide (NO) in a microfluidic platform. The CuO/Cu-MOF nanocomposite was prepared through hydrothermal method, and its formation was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS). The CuO/Cu-MOF nanostructured modified Au electrodes enabled electrocatalytic NO oxidation at 0.6 V vs. reference electrode, demonstrating linear response over a broad concentration range of 0.03-1 μM and 1-500 μM with a detection limit of 7.8 nM. The interference effect of organic molecules and common ions was negligible, and the sensing system demonstrated excellent stability. Finally, an electrochemical microfluidic NO sensor was developed to detect of NO released from cancer cells, which were stimulated by L-arginine. Furthermore, in the presence of Fe³⁺, the stressed cells produced more NO. This work offers considerable potential for its practical applications in clinical diagnostics through determination of chemical symptoms in microliter-volume biological samples. Electrochemical microfluidic NO sensor was developed for detection of NO released from cancer cells. This miniaturized device consumes less materials and provides the basis for greener analytical chemistry.