Active chemically-sensitive sensors with source follower amplifier
Methods and apparatus relating to FET arrays for monitoring chemical and/or biological reactions such as nucleic acid sequencing-by-synthesis reactions. Some methods provided herein relate to improving signal (and also signal to noise ratio) from released hydrogen ions during nucleic acid sequencing reactions.
1. An apparatus, comprising:
an array of sensors, a plurality of sensors in the array having outputs connected in common to an amplifier node, and each sensor in the plurality including:
a chemically-sensitive field effect transistor having a first conduction terminal, a second conduction terminal coupled to a first supply voltage conductor, and a sensor surface;
a first transistor having a first conduction terminal coupled to the first conduction terminal of the chemically-sensitive field effect transistor, a second conduction terminal coupled to a second supply voltage conductor, and a gate coupled to a bias voltage conductor; and
a second transistor having a gate coupled to a corresponding select voltage conductor, a first conduction terminal coupled to the first conduction terminal of the chemically-sensitive field effect transistor, and a second conduction terminal coupled to the amplifier node; and
an amplifier having an input connected to the amplifier node and an output coupled to an output conductor.
2. The apparatus of claim 1 , wherein the amplifier comprises:
a third transistor having a gate coupled to the amplifier node, a first conduction terminal coupled to a supply voltage conductor, and a second conduction terminal; and
a fourth transistor having a gate coupled to a select signal conductor, a first conduction terminal coupled to the second conduction terminal of the second transistor, and a second conduction terminal coupled to the output conductor.
3. The apparatus of claim 1 , wherein the bias voltage conductor is coupled to a bias voltage source having a level setting the first transistor in a sub-threshold mode.
4. The apparatus of claim 1 , wherein the bias voltage conductor is coupled to a bias voltage source having a level setting the first transistor in a reverse-biased diode mode.
5. The apparatus of claim 1 , wherein the first supply voltage conductor is coupled to ground, and the second supply voltage conductor is coupled to a positive supply voltage.
6. The apparatus of claim 2 , wherein the select signal conductor is a row select signal conductor.
7. The apparatus of claim 2 , wherein the select signal conductor is a row select signal conductor, and wherein the plurality of sensors includes at least four sensors.
8. The apparatus of claim 1 , wherein the chemically-sensitive field effect transistor includes a floating gate and a passivation layer, and the sensor surface is a surface of the passivation layer over the floating gate.
9. The apparatus of claim 8 , wherein a voltage on the output conductor indicates an ion-concentration of an analyte solution coupled to the floating gate via the passivation layer.
10. The apparatus of claim 1 , wherein the sensors are arranged in a column in the array and coupled to the amplifier node in response to select signals on the select voltage conductors, and a voltage on the output conductor of the amplifier is a function of a threshold voltage of the chemically-sensitive field effect transistor that is coupled to the amplifier node.
11. The apparatus of claim 1 , including a chemical sample well including the sensor surface of the chemically-sensitive field effect transistor, and a reference electrode coupled to an analyte solution in fluid flow communication with the chemical sample well.