Biomedical sensing ( Nano -bio-sensors)

1. Biomedical sensing (Nano-bio-sensors) Diego A Gomez-Gualdron Texas A&M University February 23rd, 2010

2. Introduction Sensing means becoming aware of…

3. What if I can see? Add instrumentation…

4. Sensors applications The primary goal is detect danger so an action can be taken… Pressure sensing Gas concentration sensing We need a property that correlates to what I want to measure

5. What I want to measure in medicine? The concentration of a biomarkers can tell me the nature of a disease and what stage it is in WHITE CELLS INFECTION CREATININE KIDNEY MALFUNCTION

6. Sensibility range PSA (prostate specific antigen) is a biomarker related to the existence of prostate cancer…

7. Nanosensors If I want to measure something small, I need something small…

8. Nanosensor technology LABEL-FREE LABEL In labeled technology, some sort of label has to be attached to the biomarker, which otherwise would pass by undetected…

9. Labeled technology examples labeled Non-labeled • Quantum dots • Gold nanoparticles • Radioactive inks

10. Why would I prefer a label-free approach? One fewer step to worry about (labeling) 2. I do not need a device to excite and image the sample 3. I might create a lab-on-a-chip device 4. I would end-up with point of care (POC)testing

11. Point of care testing SCENARIO A test results treatment SCENARIO B Wait results treatment

12. FET Nanosensor Based on a conventional MOSFET… Source:wikipedia

13. Proof-of concept Performed by Lieber et al (Science 293, 1289, 2001)… nanowire Science 293, 1289, 2001

14. pH Sensing It is a good start to demonstrate the sensibility to ‘superficial’ charge changes… Science 293, 1289, 2001

15. Antibody sensing Study of the biotin-streptavidin system… streptavidin biotin Science 293, 1289, 2001 250nM Unmodified SiNW d-biotin 25 pM

16. Why it works Antigens appear during disease and can be used asbiomarkers Nature has made the binding between antibodies and antigens very specific

17. A simple model Analytical Chemistry (2006), 2093-2099

18. Some thoughts • Nanowires are sensitive to the antigen-antibody binding, because the local charge transfer is a strong enough effect for the nanowire dimensions • Building nanosensors is complicated, involving either top-down approaches using sophisticated litographic techniques, or bottom up techniques • Residual effects during fabrication causes spurious effects during functioning • Find a more process friendly substitute, but that is expected to be as sensitive

19. Si Nanoribbons as nanosensors Introduced by Linnros et al (Nanoletters, 8, 3, 945-949 (2008))… It behaves like a Schottky barrier Nanoletters, 8, 3, 945-949 (2008)

20. Antibody sensing Once again, the biotin-streptavidin system is studied… the nanoribbon is functionalized with biotin (biotinalized) and the solution contains streptavidin at different concentrations… streptavidin biotin Si Nanoribbon Modified from Science 293, 1289, 2001 Nanoletters, 8, 3, 945-949 (2008)

21. Good news Only there was response to Streptavidin There is a concentration dependant response Sensitivity can be manipulated Nanoletters, 8, 3, 945-949 (2008)

22. Are we done yet? The short answer is NO!!!... The ‘long’ answer is ... For the nanosensor to be effective, the sensing has to be performed in the presence of a pure buffer solution. On the other hand, the human blood is nothing like it.

24. The device Two separate chambers. The big one has a chip functionalized with antibody-photocleavable groups. The small one has the nanosensors. chip Nature Nanotechnology, 5, 153 (2010)

25. First blood Spiked blood containing the antigens PSA (prostate cancer) and CA15.3 (breast cancer) flow into the big chamber… Nature Nanotechnology, 5, 153 (2010)

26. Wash and sunbathe The buffer solution is added to leave the chamber blood-free. UV light breaks the photocleavable-antigen pair. Nature Nanotechnology, 5, 153 (2010) Now I have a buffer solution of antigen!!!

27. The happy ending The content of the big chamber flows toward the small chamber, where sensing takes place Nature Nanotechnology, 5, 153 (2010)

28. Verifying the capture A modified ELISA test is performed Nature Nanotechnology, 5, 153 (2010)

29. The sensor Sensor geometry and behavior similar to the one reported by Linnros et al (2008) Schottsky barrier Nature Nanotechnology, 5, 153 (2010)

30. The performance The performance described in previous studies is retained

31. Conclusions • The advances in label-free nanosensing have been plausible during the last decade • Nanoribbon sensors appears to have the necessary sensitivity and are less troublesome than nanowires • The current sensitivity of nanosensors is in the appropriate range for early cancer detection

32. Specific Assessment • Fahmyet al did not performed a control with an antigen not specific to the selected antibodies. • The correlation between the introduced concentration and the captured/release concentration must be improved • An exploration of the optimal operation parameters (potentials, thickness, etc..) must be done • The technique can be assembled in a self-contained compact design

33. General assessment to the topic • Silicon nanowire/nanoribbons are ideally suited for nanosensing, due to sensitivity and ease of functionalization • A successful implementation of the technique awaits for significant advances in the detection of suitable biomarkers • Charge screening effects (Debye length) are still a point to be addressed through more clever design of the nanosensors

34. General assessments • The research for new and more sensitive materials must not be discarded • Complete charting of a disease needs more than one antigen, so improvements in microarray arrangements must be made, as well as independent signal detection • Microfluidics studies must be made to set the fluid parameters to optimize binding, diffusion effects and response times

35. References • Science 293,1289 (2001) Lieber, et al. Nanowire Nanosensors for highly Sensitive and Selective Detection of Biological and Chemical Species • Nanoletters 8, 3, 945 (2008) Linnros, et al. Silicon Nanoribbons for Electrical Detection of Biomolecules • Nature Nanotechnology, 5, 138 (2010) Fahmy, et al. Label Free biomarker detection from whole blood • Clinical Chimica Acta, 381, 93 (2007) Chan & Liang. Enzymes and related proteins as cancer biomarkers (REVIEW) • Clinical Chimica Acta, 385, 37 (2005) Jain, Nanotechnology in clinical laboratory diagnostics (REVIEW)

37. G4Rebuttal: Biomedical Sensing Diego A. Gómez-Gualdrón

38. Comments • G2: It was not mentioned in the introduction any of the design considerations for a sensor like accuracy, repeatability, resolution, hysteresis, linearity etc… A:/ I decided to make a much more friendly introduction to the topic, instead of going on technical details that might have done the introduction more obscure. Notice that a high percentage of the audience is at the undergraduate level and they are not so familiar with the nanotechnology world. I think that the audience’s academic background guarantees that they have a ‘feel’ of what to expect from a sensing device (accuracy and so on..) My main focus in the introduction was to give the audience just the necessary information to be able to follow through the presentation of the paper results. The paper results were not focused in the sensor calibration (resolution, accuracy, etc…), but on the ability to actually ‘sense’ at such small concentration.

39. Comments • G2: Some technical terms were not defined, like Schottky Barrier, nanoribbon, streptatividin, photocleavable-antigen pair, some terminology was confusing, like 1 anti-PSA, 1 anti-CA15.3… • A:/ The 2-dimensional character of the nanoribbon was mentioned in contrast to the 1-dimensional character of the nanowire. Moreover, it was pointed that this was one of the reasons why was easier to work with nanoribbons. • It was mentioned that strepatavidin/biotin is an antibody/antigen pair widely used in this kind of studies • Photo=light, Cleavable=break. A photocleavable antigen pair wherein an antigen breaks loose under UV light. This was explained since this is what enables the transfer of antigen from the ‘big’ chamber to the ‘small’ chamber • 1 anti-PSA: the antibody corresponding to the antigen PSA. Use the same reasoning for 1-anti-CA15.3 • The point of the Schottky barrier was only brought up to point the similarities of the electrical behavior of the presented nanosensor to that of a conventional Schottky barrier FET

40. Comments • G2: The microfabrication process was not illustrated, and the nanowire functionalization procedure was also not shown. The technical challenge implied on making the nanodevice and making it work was not explained… a) The focus of the presentation was centered on the functioning of the device, not on the fabrication of the devices. Therefore, only I few remarks about the fabrication process were done. b) The presentation showed three mile-stone papers on the development of nanosensors since 2001 up to date. Throughout the presentation, it was constantly discussed the challenges at-the-paper-date and the approach used in the paper to solve it. Moreover, some of these challenges were pointed to explain the transition from a nanowire- to a nanoribbon based sensor. All the three papers were about ‘making it work’. If the technical challenges refer to their fabrication, answer a) applies

41. Comments • G6: How effective are nanowires in nanoFET in detecting such charge transfer? • Nanowire technology correspond to the first paper presented. The plots shows that concentrations in the order of picomolar were detected. This corresponds to the binding of about six antigens to the functionalized nanowire. It is noteworthy, though, that this sensitivity occurs under specfic conditions. For instance, the presence of a buffer solution is a ‘must’. However, there are ways around this, as shown in the third paper

42. Comments • G6: What methods are currently being used to fabricate these nanosensors? • The use of silicon nanoribbons makes it preferable to use top-down approaches as e-beam litography and selective etching, using silicon on insulator wafers as starting materials. • G6: Could this be batch processed for cost reduction and large scale production? • Yes, but it is not the main concern just now. The current primary objective is to make the technology work properly

43. Comments • G6: What are the methods in detecting which antigen is binding with which antibody in the nano-scale sensing • If your question refers as to what antibody must the sensor be functionalized with in order to detect an specific antigen, I must say that usually labeled technology (fluorescence assays) has been traditionally used to determine what antigen binds with what antibody. However, the implementation of better biosensors like the one presented in this study significantly would speed up the screening of these pairs, which itself would help to create more selective nanosensors

44. Comments • G6: Is the number of charge transferred different for different antigen-antibody combination? • Yes, it is different because different compounds modify the electron density in the neighborhood of nanosensor surface in slightly different ways. As you can see for the rsults of the third paper, identical concentration of different antigen produces a different slope in the response curve

45. General Comments • I agree with comments pointing to the length of presentation and the use of filler words. I will work on improving my presentation skills. Also I will improve the graphic labels • There was some mixed feelings about the ‘informal approach’ used in the presentation. So I guess I will use a more formal approach in the up coming presentation

46. G1Review : Biomedical Sensing By Edson P. Bellido Sosa

47. The presenter described in detail what a bio-sensors is and what we want to detect in biomedical applications. He explained why one wants a label free detection. He analyzed 3 papers. The first is based on a silicon nanowire functionalized with amine group and bioting in a FET configuration, they measured the change in pH and he explained how the nanosensor works. In the second paper they test a silicon nanoribon and measured the change in conductivity according to the concentration of streptavidin. Finally in the third paper they used microfluidic channel technology to include a filtering step in the process of sensing, in this paper they measure the concentration of PSA and CA15.3, which are biomarkers for prostate cancer and breast cancer respectively, using the change in conductivity in a silicon array. Future research would be about the use of other nanomaterials for nanosensing to increase the sensitivity and selectivity. Also more research needs to be done in the area of design optimization of the lab on a chip structures to avoid false positives or negatives. Also other interesting area is the discovery of new biomarkers which are directly related to a disease. http://image.absoluteastronomy.com/images/encyclopediaimages/f/fr/free_psa.png

48. G2 Review Biomedical Sensing by Alfredo Bobadilla

49. Review of biomedical sensing lecture It was shown how a functionalized Si nanowire can be used for electrical detection of very low concentration of molecular biomarkers. The working principle and performance of the biosensing device was illustrated. Nevertheless it was not mentioned in the introduction any of the design considerations for a sensor like accuracy, repeatability, resolution, hysteresis, linearity, etc. Some technical terms were not defined, like Schottky barrier, nanoribbon, streptatividin, or photocleavable-antigen pair. And some molecular biology terminology was also confusing like ‘1 anti-PSA, ‘1 anti-CA15.3 which was shown together with pictures. The microfabrication process was not illustrated, and the nanowire functionalization procedure was also not shown. The technical challenge implied on making the nanodevice and making it works was not explained. Alfredo D. Bobadilla

50. G3 Review Biomedical Sensing by Mary Coan