Current　magnetic　relaxation　switching　(MRS)　sensors　for　detection　of　trace　targets　in　complex　samples　still　suffer　from　limitations　in　terms　of　relatively　low　sensitivity　and　poor　stability.　To　meet　this　challenge,　we　develop　a　longitudinal　relaxation　time　(T-1)-based　nano　sensor　by　using　Mn2+　released　from　the　reduction　of　a　MnO,　nanoassembly　that　can　induce　the　change　of　T-1,　and　thus　can　greatly　improve　the　sensitivity　and　overcome　the　＂hook　effect＂　of　conventional　MRS.　Through　the　specific　interaction　between　antigen　and　the　antibodyfunctionalized　MnO,　nanoassembly,　the　T-1　signal　of　Mn2+　released　from　the　nanoassembly　is　quantitatively　determined　by　the　antigen,　which　allows　for　highly　sensitive　and　straightforward　detection　of　targets.　This　approach　broadens　the　applicability　of　magnetic　biosensors　and　has　great　potential　for　applications　in　early　diagnosis　of　disease　biomarkers.