Quartz crystal microbalance based histidine sensor

Figures & data

Figure 1 HPLC analysis of MAH monomer (flow rate: 0.5 mL/min, methanol-water elution (80–20 v/v), wavelength: 254 nm).

Figure 2 Zeta sizer measuments of MIP (a) and NIP (b).

Figure 3 FTIR-ATR spectrum of MIP attached QCM surface.

Table 1. Contact angle measurements.

Surface	Contact Angle (^0)
Non-modified QCM gold surface	68.7
l-Histidine imprinted nanoparticle attached QCM gold surface	59.8
l-Histidine non-imprinted nanoparticle attached QCM gold surface	62.2

Figure 4 Contact angle measurements of non-modified QCM gold surface (a), MIP attached QCM gold surface (b), NIP attached QCM gold surface (c).

Figure 5 Real-time responses of MIP QCM biosensor against aqueous solutions of l-histidine at different concentrations in 10 mM phosphate buffer, pH 7.4 at a flow rate of 1.0 mL/min, (a) frequency change, (b) mass change.

Figure 6 Real-time responses of MIP QCM biosensor against aqueous solutions for l-histidine, D-histidine, l-tryptophan (a) and binary mixtures (b). Experimental conditions; pH 7.4, flow rate: 1.0 mL/min, concentration of l-histidine, d-histidine, l-tryptophan: 96.6 µM.

Figure 7 Real-time responses of NIP QCM biosensor against aqueous solutions for l-histidine, D-histidine, l-tryptophan. Experimental conditions; pH 7.4, flow rate: 1.0 mL/min, concentration of l-histidine, d-histidine, l-tryptophan: 96.6 µM.

Table 2. Selectivity and relative selectivity coefficients for l-histidine against d-histidine and l-tryptophan.

	MIP		NIP
	Δm	k	Δm	k	k'
l-Histidine	0.35		0.224
d-Histidine	0.06	5.83	0.235	0.95	6.12
l-Tryptophan	0.16	2.19	0.220	1.02	2.15

Table 3. Kinetic rate constants.

Equilibrium analysis (Scatchard)		Association kinetic analysis
Δmmaks, µM/cm^2	1.6	ka, µM/s	0.00002
KA, µM	0.002	kd, 1/s	0.0001
KD, 1/µM	500	KA, µM	0.2
R^2	0.90075	KD, 1/µM	5
		R^2	0.9336

Figure 8 Real-time responses of MIP QCM biosensor against aqueous solutions for RNAase, lysozyme, cytochrome-C, l-histidine and BSA. Experimental conditions; pH 7.4, flow rate: 1.0 mL/min, concentration of RNAase, lysozyme, cytochrome-C, l-histidine and BSA: 96.6 µM.

Figure 9 Reproducibility of MIP QCM biosensor. Experimental conditions; pH 7.4, flow rate: 1.0 mL/min, concentration of l-histidine: 96.6 µM.

Table 4. Equilibrium isotherm models.

Langmuir		Freundlich		Langmuir-Freunlich
Δmmaks, µM/cm^2	0.799	Δmmaks, µM/cm^2	0.0205	Δmmaks, µM/cm^2	2.24
KA, µM	50.52	1/n	0.7199	1/n	0.7199
KD, 1/µM	0.01979	R^2	0.92	KA, µM	0.01105
R^2	0.96			KD, 1/µM	90.49
				R^2	0.98