The Q-Sense E4 is a real-time analytical instrument for studies of molecular events occurring on surfaces. It measures mass and viscoelastic properties of molecular layers as they build up or change on the sensor surface. The instrument has four flow modules, each holding one sensor enabling four parallel measurements. The sensors oscillate at a specific frequency when voltage is applied. The frequency of the oscillation changes as the mass on the sensor changes. Turning off the voltage causes the oscillation to decay. The decay-rate or Dissipation factor is related to the elasticity and viscosity of the molecular layer on the sensor. By measuring the frequency and dissipation, it becomes possible to analyze the state of molecular layers bound to the sensor surface, their mass, thickness and structural (viscoelastic) properties.

Sensors and sample handling system

• Number of sensors: 4, also possible to measure using only 1, 2 or 3 sensors
• Volume above each sensor: 40 μl
• Minimum sample volume: 300 μl
• Working temperature: 15 to 65°C, controlled via software, stability ±0.02 K
• Typical flow rates: 50-200 μl/min
• Sensor crystals: 5 MHz, 14 mm diameter, polished, AT-cut, gold electrodes
• Set-up includes option to perform in-situ electrochemical measurements

Frequency and dissipation characteristics

• Frequency range: 1-70 MHz (allows 7 frequencies, up to the 13th overtone, 65 MHz for a 5 MHz crystal)
• Maximum time resolution, 1 sensor, 1 frequency: 200 data points per second
• Maximum mass sensitivity in liquid: 0.5 ng/cm² (5 pg/mm²)
• Normal mass sensitivity in liquid: 1.8 ng/cm² (18 pg/mm²)
• Maximum dissipation sensitivity in liquid: 0.04 x 10^-6
• Normal dissipation sensitivity in liquid: 0.1 x 10^-6
• Typical noise peak to peak (RMS) in liquid: 0.16 Hz (0.04 Hz)