Motivation: Case scenario correlating increased Troponin measurements with Acute Coronary Syndrome
“Case Presentation: J.P. is an obese 55-year-old male with a history of gastroesophageal reflux disease who presents to the emergency department with substernal chest pain that he attributes to a “large meal.” J.P. is pale and diaphoretic. An ECG shows tachycardia with normal sinus rhythm. J.P.’s troponin levels (decision limit >0.04 μg/L) at presentation and at 6 and 12 hours after presentation are 0.09, 4.41, and 19.62 μg/L, respectively.” http://www.circ.ahajournals.org/content/116/18/e501.full
“J.P.’s presentation and troponin results are consistent with the diagnosis of ACS (Figure 1A). An additional cTnI measurement, 48 hours after admission, revealed a downward trend in his troponin level. Because of the improved sensitivity and precision at low cTnI concentrations, the initial cTnI result indicated myocardial injury and the subsequent diagnosis of ACS.”
a) Acute Coronary Syndrome: Symptoms and Biomarkers
Acute coronary syndrome (ACS) is a disease attributed to obstruction of the coronary arteries. Heart attack or unstable angina are categorized as ACS. The immediate symptoms include chest pain and discomfort, pain in arms and legs, nausea, and sweating. Upon feeling any of the symptoms, it is important that patients go through the diagnostic process so that immediate care can be provided.
There are a few types of enzymes that are secreted in the serum of ACS patients. Those include “cardiac enzymes (including troponin and creatine kinase), C-reactive protein (CRP), fibrinogen, homocysteine, lipoproteins, triglycerides, brain natriuretic peptide (BNP) and prothrombin”. These proteins are released from damaged heart muscle cells into the extracellular space, from which they diffuse into the bloodstream. Creatine kinase is one of the most commonly detected enzymes for ACS. However, it is not specific to cardiac diseases. Cardiac Troponin is a heart disease specific protein. Together, the detection of both creatine kinase and cardiac troponin may be used to diagnose with ACS.
Current diagnosis of ACS is very time-demanding and unapproachable, necessitating the use of consecutive blood samples every 4-8 hours at the clinic to determine whether an upward trend in ACS biomarker concentrations is detected. Here, we describe a paper-based diagnostic technique to allow patients to assess their risk of having ACS.
b) Paper-Based Diagnostic Devices
There are several at-home diagnostic devices currently available such as glucose sensor and pregnancy tests. Glucose sensors detect the glucose levels by measuring the change in pH produced by reacting blood glucose with glucose-oxidase. This allows for range of output levels.
On the other hands, pregnancy tests take advantage of the antibody-specificity and by measuring hCG (human chorionic gonadotrophin), give a positive/negative binary output. Pregnancy tests test for the presence of hCG (the left side of the figure below) and also have a negative control region (on the right side of the figure below) that measures binding of unbound antibody to immobilized antibody to ensure that the pregnancy test is valid. The hCG-detecting region has anti-hCG bodies immobilized and binds to flowing hCG (from urine) bound to an antibody coupled to gold-nanoparticles (the antibody-gold NP complexes are built into the system and bind to hCG upon applying the urine sample to the end of the stick).
The concept is widely applied towards other diagnostic applications such as with influenza and malaria. This is a very user-friendly diagnostic device since 1. it does not require any additional laboratory measurement devices, and 2. the result is shown in binary manner and does not require any additional computations or interpretations. Disadvantage might include unspecific binding of the antibodies, low substrate concentration, and the fact that the binary system does not accurately depict detection gradients. There are a few other biosensing measurement methods such as pH change detection (inspired by pH strips) , Western blotting, and colorimetric assay  in laboratory use. Application of those methods might also lead to accessible home-based diagnostics.
Our goal is to suggest a more approachable, at home diagnostic examination method that allows patients to more easily interpret whether their symptoms are ACS-relavant, to better assess the extent of cardiac muscle damage they have, and also to serve as a basis for long-term monitoring of ACS biomarkers.
Our Proposed Idea
In order to help people better assess the severity of their heart-attack-like symptoms (ex: chest pain), we propose engineering a paper-based diagnostic platform for acute coronary syndrome to help users better assess the risks associated with their symptoms and get to the hospital on time if indicated by the diagnostic platform. Currently, many patients are unsure of whether their symptoms of chest pain are significant and hesitate in going to the hospital. Our paper-based diagnostic platform may be used in all households, and especially with at-risk patients, helping them assess their cardiac troponin and CPK levels in a highly-accessible and easy manner. Furthermore, not only will it be of use in situations of acute symptoms, but it may also be used in long-term monitoring in at-risk patients.
We imagine our paper-based diagnostic to operate accordingly:
1. The paper-based diagnostic tool itself will be a small paper strip, similar to pregnancy strips.
2. It will be composed of a microfluidic chamber/filter which separates out plasma from blood drawn from a finger prick.
3. The plasma will then be assayed for the presence of ACS biomarkers such as cardiac Troponin and CPK via signal amplification of CPK and troponin [the mechanism for this is still in making].
4. The result of the signal amplification will be detected, whether as a gradient of colors, the presence of certain bands on the diagnostic strip, etc.
5. A control band should be shown on the strip to confirm that the strip is operational.
There may be a possibility of extending our proposed device to include multiplexing (ex: of the various proteins involved in ACS).
 http://www.circ.ahajournals.org/content/116/18/e501.full: Cardiac Troponin Assays
Describes several clinical cases of patients presenting ACS-like symptoms and describes their respective troponin assay results, showing cases of a true positive, a false negative, and a differential case scenario. This paper also goes over the merits of having more sensitive and specific troponin assays, describing the performance and analytical accuracy of troponin assays ni predicting ACS conditions.
http://www.heart.org/HEARTORG/Conditions/HeartAttack/AboutHeartAttacks/Acute-Coronary-Syndrome_UCM_428752_Article.jsp# : Acute Coronary Syndrome, American Heart Association®
The webpage describes general conditions, symptoms, diagnostics and treatment of Acute Coronary Syndrome.
 http://cmr.asm.org/content/15/1/66.full :Rapid Diagnostic Tests for Malaria Parasites
The study shows a mechanisms of a rapid diagnostic tests for malaria that detects one of the malaria antigen using immunochromatographic capture procedures. The gold-nanoparticle conjugated monoclonal antibody flowing over another antigen specific antibody at detection region and antibody-specific-antibody at negative control region gives the indicator of infection as well as the indicator of successful test use. Author suggested the importance in providing cheap easy rapid-diagnostic device to Malaria since large number of patients are in less-developed countries with less access to medical trainings and laboratory equipments.
 http://pubs.rsc.org/en/content/articlepdf/2012/lc/c2lc21238b: Nanofluidic preconcentration device in a straight microchannel using ion concentration polarization
This study describes the use of nanofluidics under an electric field gradient to concentrate samples (such as blood samples). Mechanistically, this is done by balancing forces induced from pressure-driven flow (electroosmotic flow) and electrophoresis. This study has implications in concentrating biological molecules and potentially could be used towards our project as well.
 http://www.abcam.co.jp/creatine-kinase-activity-assay-kit-colorimetric-ab155901.html: Creatine Assay kit Protocol
Creatine Assay kit provided by abcam allows to detect kinase activity less than 1mU in calorimetric method in laboratory. The creatine kinase is reacted with creatine to produce phosphocreatine and ADP. The generated products are made to react with CK Enzyme Mix provided in the kit to form an intermediate which reduces a probe chemical to produce strong absorbance at 450 nm. The absorbance is measured using optical density measurement device.