Indicator displacement assays (IDAs) offer a unique and innovative approach to molecular sensing. This Tutorial review discusses the basic concepts of each IDA strategy and illustrates their use in sensing applications.

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Changes in adenosine triphosphate (ATP) and peroxynitrite (ONOO − ) concentrations have been correlated in a number of diseases including ischemia-reperfusion injury and drug-induced liver injury. Herein, we report the development of a fluorescent probe ATP-LW, which enables the simultaneous detection of ONOO − and ATP. ONOO − selectively oxidizes the boronate pinacol ester of ATP-LW to afford the fluorescent 4-hydroxy-1,8-naphthalimide product NA-OH (λ ex = 450 nm, λ em = 562 nm or λ ex = 488 nm, λ em = 568 nm). In contrast, the binding of ATP to ATP-LW induces the spirolactam ring opening of rhodamine to afford a highly emissive product (λ ex = 520 nm, λ em = 587 nm). Due to the differences in emission between the ONOO − and ATP products, ATP-LW allows ONOO − levels to be monitored in the green channel (λ ex = 488 nm, λ em = 500−575 nm) and ATP concentrations in the red channel (λ ex = 514 nm, λ em = 575−650 nm). The use of ATP-LW as a combined ONOO − and ATP probe was demonstrated using hepatocytes (HL-7702 cells) in cellular imaging experiments. Treatment of HL-7702 cells with oligomycin A (an inhibitor of ATP synthase) resulted in a reduction of signal intensity in the red channel and an increase in that of the green channel as expected for a reduction in ATP concentrations. Similar fluorescence changes were seen in the presence of SIN-1 (an exogenous ONOO − donor).

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A chiral ferrocene-based boronic acid interacts with (R)- and (S)-Binol to form two complexes that exhibit significantly different ferrocene-based electrode potentials. This difference in redox behavior can be exploited to demonstrate in principle how high levels of enantiomeric excess in a mixture of enantiomers can be quantified and read-out using an electrochemical method.