The detection of specific DNA sequences plays an important role in the identification of disease‐causing pathogens and genetic diseases, and photochemical water splitting offers a promising avenue to sustainable, environmentally friendly hydrogen production. Cobalt–phosphorus nanowires (CoP NWs) show a high fluorescence quenching ability and different affinity toward single‐ versus double‐stranded DNA. Based on this result, the utilization of CoP NWs as fluorescent DNA nanosensors with a detection limit of 100 pM and a selectivity down to single‐base mismatch was demonstrated. The use of a thrombin‐specific DNA aptamer also enabled the selective detection of thrombin. The photoinduced electron transfer from the excited dye that labels the oligonucleotide probe to the CoP semiconductor led to efficient fluorescence quenching, and largely enhanced the photocatalytic evolution of hydrogen from water under visible light. Gelöscht: Ein schneller Fluoreszenzassay für Nukleinsäuren und Proteine basiert auf der starken Fluoreszenzlöschung von Cobaltphosphid‐Nanodrähten (CoP‐NWs) und ihrer unterschiedlichen Affinität zu DNA‐Einzel‐ und DNA‐Doppelsträngen. Die Anlagerung markierter Oligonukleotidsonden an die Oberfläche eines CoP‐Halbleiters führt zur photokatalytischen Wasserstoffentwicklung aus H2O unter sichtbarem Licht.