Mesocrystals,　as　the　assemblies　of　crystallographically　oriented　nanocrystals,　have　single-crystal-like　atom　structures　and　scattering　features　but　with　much　higher　porosity　than　single-crystalline　materials,　making　them　promising　substitutes　for　conventional　single　crystals　in　photoelectrochemical　application.　As　a　proof-of-concept,　a　series　of　photoelectrochemical　tests　were　investigated　to　understand　the　influence　of　the　differences　between　them　on　photoelectrochemical　activity.　Expectedly,　comparing　with　TiO2　single　crystals,　TiO2　mesocrystals　demonstrated　higher　photoelectrochemical　capability,　which　provides　unique　new　opportunities　for　materials　design　in　the　fields　of　solar-energy　conversion　and　catalysis.　Therefore,　an　elegant　photoelectrochemical　biosensing　platform　was　firstly　developed　by　virtue　of　carbon　nanohorns　with　outstanding　electrical　conductivity　support　multifunctional　TiO2　mesocrystals　to　accelerate　the　transfer　of　photogenerated　electrons,　and　then　horseradish　peroxidase　was　introduced　through　the　immune　recognition　reaction　for　enzyme-assisted　in　situ　generating　CdS　QDs.　The　multiplex　amplification　strategy　successfully　achieved　the　ultrasensitive　detection　of　α-fetoprotein　antigen.　Promisingly,　the　successful　application　of　multiplex　amplification　strategy　affords　a　rational　and　practical　consideration　for　the　fabrication　of　new　and　high-performance　photoelectrochemical　sensing　devices.　©　2015　Elsevier　B.V.