Advanced drug development and manufacturing
X-ray fluorescence (XRF) spectrometry has been used for detecting binding events and measuring binding selectivities between chemicals and receptors. XRF may also be used for estimating the therapeutic index of a chemical. For estimating the binding selectivities of a chemical versus chemical analogs, for measuring post translational modification of proteins, and for drug manufacturing.
1. A method for estimating, in a sample, binding of a chemical having at least one heavy element of atomic number nine or higher to a biological receptor, comprising:
depositing the biological receptor on a focusing chip, wherein the focusing chip has an amount of the at least one heavy element that produces less than 25% of an X-ray fluorescence signal produced by the sample when both the focusing chip and the sample are measured for the at least one heavy element, the focusing chip being disposed on a solid metal substrate that has a thickness of less than 50 microns, wherein the focusing chip has a thickness of less than 50 microns;
acquiring a first X-ray fluorescence signal due to any presence of the at least one heavy element in the receptor disposed on the focusing chip, as a result of exposing the receptor to a first excitation X-ray beam, prior to exposing the receptor to the chemical;
exposing the receptor to the chemical by depositing the chemical onto the focusing chip, and allowing the chemical to bind to the receptor to form a chemical-receptor complex;
measuring, with an X-ray source, a second X-ray fluorescence signal due to any presence of the at least one heavy element by exposing the chemical-receptor complex to a second excitation X-ray beam, Wherein a cross section of the second excitation X-ray beam transmitted by the X-ray source is between 25% and 250% of an area of the focusing chip occupied by the receptor-chemical complex; and
subtracting the first X-ray fluorescence signal from the second X-ray fluorescence signal to quantify the binding of the chemical to the receptor, thereby estimating binding of the chemical to the receptor.
2. The method of claim 1 , further comprising standardizing result of the quantification of the binding of the chemical to the receptor by dividing the result of the quantification of the binding of the chemical to the receptor by the amount of the receptor to obtain a standardized result of the quantification of the binding of the chemical to the receptor.
3. The method of claim 1 , wherein the first or second X-ray fluorescence signal is provided using a polychromatic X-ray source.
4. The method of claim 1 , wherein the focusing chip comprises beryllium, carbon, silicon, aluminum, iron, cobalt or gold.
5. The method of claim 1 , wherein the biological receptor is selected from the group consisting of a protein, a DNA, an RNA, a human cell, a plant cell, an animal cell, and a microorganism.
6. The method of claim 1 , wherein the chemical to be measured comprises at least one of fluorine, phosphorous, sulfur, chlorine, bromine, iodine, platinum, copper, zinc, gallium, or gadolinium.
7. The method of claim 1 , wherein, in order to reduce noise, the focusing chip is substantially free of the at least one heavy element to be measured, and wherein the focusing chip is substantially free of technetium, thorium, and uranium.
8. The method of claim 1 , wherein the focusing chip is substantially free of at least one of the heavy elements selected from the group consisting of sulfur, fluorine, phosphorous, chlorine, bromine, iron, zinc, magnesium, calcium, titanium, scandium, and platinum.
9. The method of claim 1 , further comprising exposing the chemical and chemical-receptor complex to a buffer that is selected to be substantially free of the at least one heavy element present in the chemical to be measured; and wherein the buffer comprises one or more of chemicals or functional groups selected from the group consisting of amine, imine, nitrate anion nitrite anion, ammonium cation, and iminium cation.
10. The method of claim 1 , wherein the chemical-receptor complex is exposed to a solution prior to measurement of the second X-ray fluorescence the solution comprising a matrix modifier.
11. The method of claim 1 , wherein the second X-ray fluorescence signal is measured using a chromium, palladium or silver X-ray source.
12. The method of claim 1 , wherein the second X-ray fluorescence signal is measured using a rhodium source or a molybdenum source.
13. The method of claim 1 , wherein the second X-ray fluorescence signal is measured using an X-ray source having a K-alpha L-alpha line at or above 2.838 KeV and less than 9.441 KeV.
14. The method of claim 1 , wherein the receptor is deposited on the focusing chip in volumes between 1 nanoliter and 50 microliters.
15. The method of claim 1 , wherein the chemical receptor complex is concentrated on the focusing chip prior to measurement of the second X-ray fluorescence signal.
16. The method of claim 1 , wherein the sample contains between ten nanograms and one microgram of the at least one heavy element.
17. The method of claim 1 , wherein the focusing chip has a pattern of at least one hydrophobic region and at least one hydrophilic region.
18. The method of claim 1 , further comprising selecting the focusing chip based on the at least heavy element to be measured in the chemical-receptor complex by:
for measurement of the heavy element phosphorus, selecting a focusing chip that is substantially free of zirconium, platinum, gold, niobium, mercury, and thallium;
for measurement of the heavy element sulfur, selecting a focusing chip that is substantially free of thallium, molybdenum, sulfur, lead, bismuth, technetium, and ruthenium; and
for measurement of the heavy element chlorine, selecting a focusing chip that is substantially free of technetium, ruthenium, rhodium and palladium.