The　growth　of　gold　nanobipyramids　(AuNBPs)　provides　a　superior　colorimetric　quantification　method　for　point-of-care　testing　due　to　their　superior　growth　uniformity,　high-resolution　multicolor　response,　and　excellent　seed　storage　stability.　However,　conventional　growth　methods　face　significant　limitations　in　sensing　applications　due　to　their　reliance　on　a　single　reductant　and　stringent　acidic　conditions.　This　study　systematically　investigated　the　reductant　mechanism　in　AuNBP　growth,　revealing　that　the　pH-regulated　redox　potential　is　crucial　for　achieving　anisotropic　AuNBP　growth.　By　employing　nine　different　reductants,　the　growth　pH　was　expanded　from　1.5　to　8.5.　Notably,　dihydroxybenzene-mediated　systems　exhibited　a　slender　morphology,　reduced　reductant　consumption,　enhanced　stability,　and　comparable　analytical　performance　compared　to　the　conventional　growth　system.　Among　these　systems,　the　hydroquinone　(HQ)-mediated　system　was　integrated　with　horseradish　peroxidase　(HRP)-catalyzed　reactions　in　a　pH-compatible　manner.　By　incorporating　this　integrated　system　into　a　commercial　HRP　immunoassay,　a　novel　multicolor　immunosensor　was　developed　for　thyroglobulin　(Tg)　detection.　This　immunosensor　exhibited　a　distinct　nine-color　gradient　across　a　ten-fold　Tg　concentration　range　(0.1–1.3　ng/mL),　achieving　a　visual　detection　limit　of　0.1　ng/mL　and　an　instrumental　detection　limit　of　29　pg/mL.　It　accurately　detected　Tg　in　human　serum　with　good　recoveries　of　94.1　%-104.8　%　and　signal　stability　for　six　hours.　The　results　correlated　well　with　the　commercial　immunoassay　while　offering　superior　visual　readout　for　point-of-care　settings.　These　findings　validate　the　applicability　of　the　HQ-mediated　system　in　converting　conventional　single-color　HRP　immunoassays　to　multicolor　immunosensors.　Furthermore,　expanding　reductant　selection　and　pH　adaptability　in　AuNBP　growth　offers　more　possibilities　for　developing　versatile　pH-flexible　multicolor　sensors.　©　2025　Elsevier　B.V.