Toward point-of-care management of chronic respiratory conditions:Electrochemical sensing of nitrite content in exhaled breath condensate using reduced graphene oxide

We present a portable non-invasive approach for measuring indicators of inflammation and oxidative stress in the respiratory tract by quantifying a biomarker in exhaled breath condensate(EBC).We discuss the fabrication and characterization of a miniaturized electrochemical sensor for detecting nitrite content in EBC using reduced graphene oxide.The nitrite content in EBC has been demonstrated to be a promising biomarker of inflammation in the respiratory tract,particularly in asthma.We utilized the unique properties of reduced graphene oxide(rGO);specifically,the material is resilient to corrosion while exhibiting rapid electron transfer with electrolytes,thus allowing for highly sensitive electrochemical detection with minimal fouling.Our rGO sensor was housed in an electrochemical cell fabricated from polydimethyl siloxane(PDMS),which was necessary to analyze small EBC sample volumes.The sensor is capable of detecting nitrite at a low over-potential of 0.7 V with respect to an Ag/AgCl reference electrode.We characterized the performance of the sensors using standard nitrite/buffer solutions,nitrite spiked into EBC,and clinical EBC samples.The sensor demonstrated a sensitivity of 0.21μAμM^(−1) cm^(−2) in the range of 20–100μM and of 0.1μAμM^(−1) cm^(−2) in the range of 100–1000μM nitrite concentration and exhibited a low detection limit of 830 nM in the EBC matrix.To benchmark our platform,we tested our sensors using seven pre-characterized clinical EBC samples with concentrations ranging between 0.14 and 6.5μM.This enzyme-free and label-free method of detecting biomarkers in EBC can pave the way for the development of portable breath analyzers for diagnosing and managing changes in respiratory inflammation and disease.

Toward point-of-care assessment of patient response:a portable tool for rapidly assessing cancer drug efficacy using multifrequency impedance cytometry and supervised machine learning

We present a novel method to rapidly assess drug efficacy in targeted cancer therapy,where antineoplastic agents are conjugated to antibodies targeting surface markers on tumor cells.We have fabricated and characterized a device capable of rapidly assessing tumor cell sensitivity to drugs using multifrequency impedance spectroscopy in combination with supervised machine learning for enhanced classification accuracy.Currently commercially available devices for the automated analysis of cell viability are based on staining,which fundamentally limits the subsequent characterization of these cells as well as downstream molecular analysis.Our approach requires as little as 20μL of volume and avoids staining allowing for further downstream molecular analysis.To the best of our knowledge,this manuscript presents the first comprehensive attempt to using high-dimensional data and supervised machine learning,particularly phase change spectra obtained from multi-frequency impedance cytometry as features for the support vector machine classifier,to assess viability of cells without staining or labelling.

Fully integrated wearable impedance cytometry platform on flexible circuit board with online smartphone readout

We present a wearable microfluidic impedance cytometer implemented on a flexible circuit wristband with on-line smartphone readout for portable biomarker counting and analysis.The platform contains a standard polydimethylsiloxane(PDMS)microfluidic channel integrated on a wristband,and the circuitry on the wristband is composed of a custom analog lock-in amplification system,a microcontroller with an 8-bit analog-to-digital converter(ADC),and a Bluetooth module wirelessly paired with a smartphone.The lock-in amplification(LIA)system is implemented with a novel architecture which consists of the lock-in amplifier followed by a high-pass filter stage with DC offset subtraction,and a post-subtraction high gain stage enabling detection of particles as small as 2.8μm using the 8-bit ADC.The Android smartphone application was used to initiate the system and for offline data-plotting and peak counting,and supports online data readout,analysis,and file management.The data is exportable to researchers and medical professionals for in-depth analysis and remote health monitoring.The system,including the microfluidic sensor,microcontroller,and Bluetooth module all fit on the wristband with a footprint of less than 80 cm2.We demonstrate the ability of the system to obtain generalized blood cell counts;however the system can be applied to a wide variety of biomarkers by interchanging the standard microfluidic channel with microfluidic channels designed for biomarker isolation.

A microwell-based impedance sensor on an insertable microneedle for real-time in vivo cytokine detection

Impedance-based protein detection sensors for point-of-care diagnostics require quantitative specificity,as well as rapid or real-time operation.Furthermore,microfabrication of these sensors can lead to the formation of factors suitable for in vivo operation.Herein,we present microfabricated needle-shaped microwell impedance sensors for rapid-sample-to-answer,label-free detection of cytokines,and other biomarkers.The microneedle form factor allows sensors to be utilized in transcutaneous or transvascular sensing applications.In vitro,experimental characterization confirmed sensor specificity and sensitivity to multiple proteins of interest.Mechanical characterization demonstrated sufficient microneedle robustness for transcutaneous insertion,as well as preserved sensor function postinsertion.We further utilized these sensors to carry out real-time in vivo quantification of human interleukin 8(hIL8)concentration levels in the blood of transgenic mice that endogenously express hIL8.To assess sensor functionality,hIL8 concentration levels in serum samples from the same mice were quantified by ELISA.Excellent agreement between real-time in vivo sensor readings in blood and subsequent ELISA serum assays was observed over multiple transgenic mice expressing hIL8 concentrations from 62 pg/mL to 539 ng/mL.