Quantifying Nanoparticles by DNA-Driven Nanochemical Titration

Nanosynthesis has delivered an expanding library of nanomaterial reagents with rich functions surpassing those of their atomic/molecular counterparts. However, there is a lack of a chemical method capable of measuring the molar concentrations of structurally/compositionally complicated nanoparticles. We herein present a general way to determine the molar extinction coefficients of nanoparticles without even needing their compositional/morphological information, inspired by traditional chemical titration. DNA-programmable assembly is employed to drive titrant and analyte nanoparticles "reactive" toward each other to form heterodimers (featuring uncoupled and additive spectral properties) in a stringent 1:1 stoichiometry, followed by spectral deconvolution to obtain the molar extinction coefficients of nanoparticle analytes. The method is straightforward in principle and robust against common errors due to adsorptive or precipitative nanoparticle losses. Most importantly, the titration-based strategy inherently guarantees correct and cross-checkable stoichiometric ratios between nanoparticles, offering a long-sought capability to unify nanoparticles' molar extinction coefficients obtained in different laboratories when perfectly shaped Au nanospheres are employed as common titrants.