BIOMEDICAL SENSING (Nano-bio-sensors)

Diego A Gomez-GualdronTexas A&M University

February 23rd, 2010

IntroductionSensing means becoming aware of…

What if I can see?Add instrumentation…

Sensors applicationsThe primary goal is detect danger so an action can be taken… Pressure sensingGas concentration

sensing

We need a property that correlates to what I want to measure

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

Sensibility range

Antigen Concentration Organ Confinement

PSA 4-10 ng/ml 75%

PSA >10ng/ml >50%

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

Nanosensors

If I want to measure something small, I need

something small…

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…

Labeled technology examples

• Quantum dots

• Gold nanoparticles

• Radioactive inks

labeled Non-labeled

Why would I prefer a label-free approach?

1. 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

Point of care testing

test results treatment

SCENARIO A

SCENARIO B

Wait results treatment

FET Nanosensor

Based on a conventional MOSFET…

Source:wikipedia

Proof-of conceptPerformed by Lieber et al (Science 293, 1289, 2001)…

nanowire

Science 293, 1289, 2001

pH SensingIt is a good start to demonstrate the sensibility to

‘superficial’ charge changes…

Science 293, 1289, 2001

Antibody sensingStudy of the biotin-streptavidin system…

biotin

streptavidin

Science 293, 1289, 2001

250nM Unmodified SiNW

d-biotin 25 pM

Why it worksAntigens appear during disease and can be used as biomarkers

Nature has made the binding between antibodies and antigens very specific

A simple model

Analytical Chemistry (2006), 2093-2099

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

Si Nanoribbons as nanosensorsIntroduced by Linnros et al (Nanoletters, 8, 3, 945-949 (2008))…

Nanoletters, 8, 3, 945-949 (2008)

It behaves like a Schottky barrier

Antibody sensingOnce again, the biotin-streptavidin system is studied… the nanoribbon is functionalized with biotin (biotinalized) and the solution contains streptavidin at different concentrations…

biotin

streptavidin

Si Nanoribbon

Nanoletters, 8, 3, 945-949 (2008)

Modified from Science 293, 1289, 2001

Good newsOnly there was response to

StreptavidinThere is a concentration dependant

response

Sensitivity can be manipulated

Nanoletters, 8, 3, 945-949 (2008)

Are we done yet?

The short answer is NO!!!...

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.

The ‘long’ answer is ...

The deviceTwo 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)

First bloodSpiked blood containing the antigens PSA (prostate cancer) and CA15.3 (breast cancer) flow into the big chamber…

Nature Nanotechnology, 5, 153 (2010)

Wash and sunbatheThe buffer solution is added to leave the chamber blood-free. UV light breaks the photocleavable-antigen pair.

Now I have a buffer solution of antigen!!!

Nature Nanotechnology, 5, 153 (2010)

The happy endingThe content of the big chamber flows toward the small chamber, where sensing takes place

Nature Nanotechnology, 5, 153 (2010)

Verifying the capture

Nature Nanotechnology, 5, 153 (2010)

A modified ELISA test is performed

The sensorSensor geometry and behavior similar to the one reported by Linnros et al (2008)

Schottsky barrier

Nature Nanotechnology, 5, 153 (2010)

The performanceThe performance described in previous studies is retained

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

Specific Assessment• Fahmy et 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

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

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

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)

G4Rebuttal: Biomedical Sensing

Diego A. Gómez-Gualdrón

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.

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

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

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

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

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

• 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

Comments

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

G1Review : Biomedical Sensing

By Edson P. Bellido Sosa

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

G2

Review Biomedical Sensingby Alfredo Bobadilla

It was shown how a functionalized Si nanowire can be used for electrical detection of very low concentration of molecularbiomarkers. 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 withpictures.

The microfabrication process was not illustrated, and thenanowire functionalization procedure was also not shown.The technical challenge implied on making the nanodevice andmaking it works was not explained.

Alfredo D. Bobadilla

Review of biomedical sensing lecture

G3

Review Biomedical Sensingby Mary Coan

ReviewReview

Overall a great presentationNanosensors are used for early cancer

detectionNanosensors using nanoribbons are more

easily fabricated than nanowires and have similar sensitivity

Explained in detail sensors and nanosensors◦Graphics were used as aids

ReviewReview

Presented a significant amount of information about bio-nanosensors in a fun and educational way

Assessment of the paper and topic was spot on

G5Review Biomedical Sensing

by Norma Rangel

Biomedical sensing (Nano-bio-sensors), by Diego A. Gomez-Gualdron

• Diego did a very educational and organized presentation about sensors for biomedical applications, with an emphasis on biomarkers used to detect cancer.

• The presentation is very self explanatory and didactic, the papers chosen are state of the art and very promising for early detection because they are able to detect in concentrations in the range of 4-10 ng/ml

G6

Review Biomedical SensingBy Jung Hwan Woo

How effective are nanowires in nanoFET in detecting such charge transfer?What methods are currently being used to fabricate these nanosensors? E-beam litho? X-ray? Could these be batch processed for cost reduction and large-scale production?

Jung Hwan Woo

What are the methods in detecting which antigen is binding with which antibody in the nano-scale sensing? Is the number of transferred charge different for different antigen-antibody combination?