As a prototype of a ‐ detecting technique, a silicon nanowire‐based (SiNW‐based) sensor for endogenous hypochlorite in a macrophage is constructed. The sensor for hypochlorite is prepared by decorating a near‐infrared dye, IR780 onto the surface of SiNWs. The sensor exhibits high sensitivity and linear dependence of the intensities on the hypochlorite concentrations. With the help of micromanipulation and laser scanning confocal microscopy, detection of endogenous hypochlorite in a macrophage is realized by penetrating the SiNW‐based sensor into individual . The current SiNW‐based sensor will possess potential value in revealing the role of hypochlorite in physiology and pathology. Such ‐ detecting techniques can be expanded to other fields. This work will open a new door to a variety of novel studies by combining the strengths of ‐ detecting techniques with biology.