A neutral polyfluorene derivative, poly(9,9-bis(6'-benzimidazole) hexyl) fluorene-alt-1,4-phenylene (PBP), is synthesized and well characterized by H-1 NMR, C-13 NMR, and GPC. PBP exhibits exemplary activity as noninvasive fluorescence sensor and accomplishes in situ monitoring of important biological targets like Fe3+ and inorganic phosphates in saliva. On binding Fe3+, the fluorescence of PBP is quenched by 97% in label free conditions. The fluorescence of PBP is regained back on adding inorganic phosphate with a fluorescence enhancement of 106% due to the displacement of Fe3+ from the PBP. This PBP assay is further used to detect and estimate inorganic phosphate in fresh saliva samples which is also able to enhance the fluorescence by >94%. This ability of PBP to accomplish in situ monitoring and estimation of indispensable biological targets like Fe3+ and inorganic phosphates rapidly, at very low concentration with very high selectivity corroborates the extension of this assay system for safe clinical applications.