Molecule mass detection via field emission of electrons from membranes
An active detector and methods for detecting molecules, including large molecules such as proteins and oligonucleotides, at or near room temperature based on the generation of electrons via field emission (FE) and/or secondary electron emission (SEE). The detector comprises a semiconductor membrane having an external surface that is contacted by one or more molecules, and an internal surface having a thin metallic layer or other type of electron emitting layer. The kinetic energy of molecules contacting the semiconductor membrane is transferred through the membrane and induces the emission of electrons from the emitting layer. An electron detector, which optionally includes means for electron amplification, is positioned to detect the emitted electrons.
1. A detector for detecting molecules, said detector comprising:
a semiconductor membrane having an external surface for receiving said molecules, and an internal surface positioned opposite to said external surface, wherein said semiconductor membrane has a thickness of 5 nanometers to 50 microns;
an electron emitting layer comprising a material selected from the group consisting of metals, doped semiconductors and doped diamond materials provided on the internal surface of said semiconductor membrane, wherein said emitting layer is a single continuous layer provided on the internal surface of said semiconductor membrane and has a thickness of 5 nanometers to 10 microns, wherein the semiconductor membrane and emitting layer combine to provide a uniform combined thickness that does not vary by more than 20% over an active area of the detector, and wherein said emitting layer emits electrons when said semiconductor membrane receives said molecules; and
an electron detector positioned to detect at least a portion of said emitted electrons.
2. The detector of claim 1 wherein said emitting layer is electrically biased by applying a voltage of −3000 V to 3000 V to said emitting layer.
3. The detector of claim 1 wherein said emitting layer has a thickness of 5 nanometers to 25 nanometers.
4. The detector of claim 1 wherein said emitting layer is a metallic layer that conformally coats at least a portion of the internal surface of said semiconductor membrane.
5. The detector of claim 1 wherein said semiconductor membrane is provided at temperature of 2 K to 600 K.
6. The detector of claim 1 wherein said semiconductor membrane comprises one or more semiconductor materials selected from the group consisting of Si, Ge, SiN, diamond-on-insulator semiconductors, and combinations thereof.
7. The detector of claim 1 wherein said external surface of said semiconductor membrane is electrically biased by applying a voltage of −2000 V to 2000 V to said semiconductor membrane.
8. The detector of claim 1 wherein said semiconductor membrane comprises a plurality of layers of one or more semiconductor materials, wherein each of said layers have thicknesses of 1 nanometer to 1000 nanometers.
9. The detector of claim 1 further comprising a substrate having one or more active detector areas, wherein each active detector area comprises said semiconductor membrane and said emitting layer, wherein the semiconductor membrane of each active detector area has a surface area of 0.1 milimeters 2 to 20 2 centimeters 2 .
10. The detector of claim 1 wherein said semiconductor membrane has a thickness of 50 nanometers to 300 nanometers.
11. The detector of claim 1 wherein said emitting layer and internal surface of the semiconductor membrane are substantially flat having said uniform combined thickness that does not vary by more than 5% over the active area of the detector.
12. The detector of claim 1 further comprising an electrode positioned between said inner surface of said membrane and said electron detector.
13. The detector of claim 12 wherein said electrode is a grid electrode electrically biased by applying a voltage of −2000 V to 2000 V to said electrode.
14. The detector of claim 1 wherein said semiconductor membrane further comprises a protective layer provided on the external surface, wherein said protective layer has a thickness of 5 nanometers to 25 nanometers.
15. The detector of claim 1 wherein said electron detector comprises one or more microchannel plate or dynode positioned in the path of electrons emitted by said emitting layer.
16. The detector of claim 15 wherein said electron detector further comprises a photoluminescent screen and photodetector, wherein said photoluminescent screen receives said electrons from said resonators and generates electromagnetic radiation which is detected by said photodetector.
17. The detector of claim 1 further comprising a mass analyzer selected from the group consisting of a quadrupole mass analyzer, magnetic sector mass analyzer, time of flight mass analyzer, and ion trap mass analyzer.
18. A method for detecting molecules comprising the steps of:
providing a detector comprising:
a semiconductor membrane having an external surface for receiving said molecules, and an internal surface positioned opposite to said external surface, wherein said semiconductor membrane has a thickness of 5 nanometers to 50 microns;
an electron emitting layer comprising a material selected from the group consisting of metals, doped semiconductors and doped diamonds provided on the internal surface of said semiconductor membrane, wherein said emitting layer is a single continuous layer provided on the internal surface of said semiconductor membrane and has a thickness of 5 nanometers to 10 microns, wherein the semiconductor membrane and emitting layer combine to provide a uniform combined thickness that does not vary by more than 20% over an active area of the detector, and wherein said emitting layer emits electrons when said semiconductor membrane receives said molecules;
contacting said molecules with the external surface of said membrane, thereby generating electrons emitted by said emitting layer; and
detecting the emitted electrons.
19. The method of claim 18 further comprising electrically biasing said emitting layer, said semiconductor layer or both so as to generate field emission, secondary electron emission or both from said emitting layer.
20. A method of detecting molecules comprising the steps of:
a) providing a detector having active detector areas, wherein each active detector area comprises:
a semiconductor membrane having an external surface for receiving said molecules, and an internal surface positioned opposite to said external surface, wherein said semiconductor membrane has a thickness of 5 nanometers to 50 microns;
an electron emitting layer comprising a material selected from the group consisting of metals, doped semiconductors and doped diamonds provided on the internal surface of said semiconductor membrane, wherein said emitting layer is a single continuous layer provided on the internal surface of said semiconductor membrane and has a thickness selected of 5 nanometers to 10 microns, wherein the semiconductor membrane and emitting layer combine to provide a uniform combined thickness that does not vary by more than 20% over an active area of the detector, and wherein said emitting layer emits electrons when said semiconductor membrane receives said molecules;
b) contacting said molecules with the external surface of said semiconductor membrane;
c) converting the kinetic energy of said molecules contacting the external surface into lattice vibrations of the semiconductor membrane to generate phonons;
d) transferring said phonons to said emitting layer, thereby generating electrons from the emitting layer in response to said transfer of phonons; and
e) detecting the electrons emitted by said emitting layer.