Lifetime Probes

		Excitation Light Sources												Characteristics						Characteristics
Product Number (Specs Sheet)	Product Name (Product Info)	380	405	436	488	532	594	635	650	680	700	750	780	Medium	λ abs [nm]	ε [M ^–1 cm^–1]	λ em [nm]	QY [%]	FLT [ns]	Medium	λ abs [nm]	ε [M^–1 cm^–1]	λ em [nm]	QY [%]	FLT [ns]	Buy

K6-207 K6-207	3-DAB 3-DAB		•	•	•									Toluene	445	9,700	582	43		EtOH	460	8,600	665	22	4.0
K8-1350 K8-1350	Square-670-Carboxy Square-670-Carboxy	•	•					•	•					PB 7.4	656		676	1.7	0.29	6g/L BSA	673		693	29
K8-1351 K8-1351	Square-660-Carboxy Square-660-Carboxy	•	•					•	•					PB 7.4	657	182,000	676	3	0.27	2g/L BSA	679	182,000	696	45	3.56
K8-1405 K8-1405	Square-650-pH-Carboxy Square-650-pH-Carboxy						•	•	•					PB 5.6	653	135,000	671	16	1.17	pH 9.0	535	48,000	663	9	0.53

Probes such as Square-660-Carboxy show large changes in FLT upon binding to either proteins or cell-surfaces. Square-660-Carboxy is water-soluble but with a strong affinity for hydrophobic regions of biomolecules. Its lifetime increases from 0.27 ns (free in solution) up to 3.56 ns in presence of 6 mg/mL BSA and 3.32 ns when covalently bound to BSA.

Comparison of the frequency responses of
Square-660-Carboxy before and after binding to BSA.
(τ_free = 270 ps; τ_{BSA bound} = 3.32 ns)

Comparison of the intensity decays of
Square-660-Carboxy before and after binding to BSA.
(τ_free = 270 ps; τ_{BSA bound} = 3.32 ns)

Square-650-pH-Carboxy is a NIR probe that exhibits a pKa around 7 and is therefore useful for measurement of pH changes in the physiologically relevant pH range from pH 6.5 to pH 8. Importantly both forms (protonated as well as unprotonated) are fluorescent and they exhibit different lifetimes which makes this compound also useful for lifetime-based applications (see Figure below). For more information about these dyes we refer you to the specs sheet of Square-650-pH-Carboxy and the published literature.

Frequency–response curves (phase angle and demodulation)
of the Square-650-pH-IgG conjugate (D/P = 0.8) at pH 2.0 and pH 9.0

pH dependent changes in Phase Angles
of Square-650-pH at 100 MHz

For more information about lifetime probes we refer you to lifetime applications.

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