Hongmiao Ji

An electrical biosensor for the detection of circulating tumor cells

In this report, we demonstrate a semi-integrated electrical biosensor for the detection of rare circulating tumor cells (CTCs) in blood. The sample was first enriched through a combination of immunomagnetic isolation and size filtration. The integration of both methods provided a high enrichment performance with a recovery rate above 70%, even for very low numbers of cancer cells present in the original sample (10 spiked MCF7 cells in 0.5 mL of blood). In the same system, the sample was then transferred to a microchip for further magnetic concentration, followed by immunochemical trapping and electronic detection by impedance spectroscopy. Three levels of spiked CTC number (30±2, 124±29, 273±23) in 10 μL of filtered blood sample were distinguished by monitoring the impedance change of the microelectrode array (MEA). The integration of different functions in a single system provided a methodology to process milliliter-sized blood samples at the macroscale and interface with the microdimensions of a highly sensitive electronic detector. The results showed that the whole system was able to detect different levels of spiked cancer cells without the use of time- and cost-intensive fluorescence labeling and image analysis. This has the potential to provide clinicians with a standalone system to monitor changes in CTC numbers throughout therapy conveniently and frequently for efficient cancer treatments.

An integrated chip for rapid, sensitive, and multiplexed detection of cardiac biomarkers from fingerprick blood.

Cardiovascular diseases are the major cause of death among adults worldwide. Electrocardiogram (ECG) is a first test when a patient suffering from chest pain sees a doctor, however, it is lack of the required sensitivity. Standard assays to detect cardiac biomarkers, like enzyme-linked immunosorbent assay (ELISA) are sensitive, but suffer from important sample and reagent consumption in large-scale studies. Moreover they are performed in central laboratories of clinics and hospitals and take a long time, which is highly incompatible with the quick decisions needed to save a heart attack patient. Herein, we describe an integrated chip allowing rapid, sensitive, and simultaneous analysis of three cardiac biomarkers in fingerprick blood. The integrated chip is composed of a filtration chip for plasma separation from blood and a silicon nanowire (SiNW) array sensor chip for protein detection. These two chips are fabricated separately and bonded to form a single unit after alignment. The integrated chip is capable of reducing the dead volume of the sample by eliminating the tubing between the two chips. After the plasma is filtrated by the filtration chip, the SiNW sensor, spotted with three different antibodies, enabled us to detect three cardiac biomarkers, troponin T (cTnT), creatine kinase MM (CK-MM) and creatine kinase MB (CK-MB), simultaneously. The integrated chip is able to attain a low detection limit of 1 pg/ml for the three cardiac biomarkers from 2 μl blood in 45 min.

Preparation of a SERS substrate and its sample-loading method for point-of-use application

A simple approach was demonstrated to prepare a silver (Ag) nanoparticle (NP) assembly as a SERS substrate. Just by dipping a flat silicon (Si) wafer into an aqueous deposition solution of hydrogen fluoride (HF) + silver nitrate (AgNO3), a monolayer of Ag NPs was uniformly deposited onto the Si wafer surface. In order to load the to-be-detected sample onto the as-prepared SERS substrate, three methods have been individually tested, (i) by incubating the SERS substrate in the sample solution, (ii) by dropping and drying a small volume of the sample solution (1-2 microl) onto the SERS substrate surface, or (iii) by directly introducing the sample into the deposition solution. The last approach was also employed to metalize a Si nanowire (NW). Due to the NWs highly curved surface, the Ag NPs self-assembled and aggregated along the NW with a close interdistance. The aggregated Ag NPs on the NW surface can also be used as a SERS substrate. The demonstrated approach holds the promise to prepare a fresh SERS substrate at the point-of-use with the sample already loaded to promptly collect the SERS signal for the field application.

A Continuous flow micro filtration device for plasma/blood separation using submicron vertical pillar gap structures

This work demonstrates a continuous flow plasma/blood separator using a vertical submicron pillar gap structure. The working principle of the proposed separator is based on size exclusion of cells through cross-flow filtration, in which only plasma is allowed to pass through submicron vertical pillars located tangential to the main flow path of the blood sample. The maximum filtration efficiency of 99.9% was recorded with a plasma collection rate of 0.67 µl min −1 for an input blood flow rate of 12.5 µl min −1 . The hemolysis phenomenon was observed for an input blood flow rate above 30 µl min −1 . Based on the experimental results, we can conclude that the proposed device shows potential for the application of on-chip plasma/ blood separation as a part of integrated point-of-care (POC) diagnostics systems.

Electrochemical detection of oligonucleotide by attaching redox probes onto its backbone

An approach was demonstrated to detect oligonucleotide by attaching redox probes onto its backbone. First, peptide nucleic acid (PNA) with a neutral backbone was immobilized onto a gold (Au) electrode surface as a capture. Second, when the PNA capture hybridized with a target oligonucleotide (a short DNA), an assembly of Au-PNA-DNA formed and phosphate groups were thus brought into the assembly from the DNAs backbone. The linker ion of Zr(4+) exhibits a strong coordination interaction with the phosphate group and the carboxylic group. The hybridized target DNA provides the phosphate group while a derivatized redox probe of ferrocene (Fc) carboxyl acid offers the carboxylic group. Therefore, the redox probe can be attached to the phosphate group by the linker to form an assembly of Au-PNA-DNA-Zr-Fc. Its redox process was studied and the detection conditions of oligonucleotide were optimized. A limit of detection of 1.0×10(-12) M or ∼2 attomol was reached.

Development of microfluidic device and system for breast cancer cell fluorescence detection

A biomicrofluidic device and a compact cellular testing system were developed to be used in cancer diagnostics. The device was fabricated by lithography-based microfabrication techniques, followed by two-step etching of deep reactive ion etching, and channels were formed by anodic bonding of Si and Pyrex. The device is based on the capture of cells inside a new meandering weir-type filter design, followed by detection and characterization using specific fluorescent labeling. Breast cancer cells MCF-7 and control cells MCF-10A were flowed through the microfluidic channels, and captured by meandering weir-type filters. 17β-Estradiaol(E2)-BSA (bovine serum albumin)-FITC (fluorescein isothiocyanate) macromolecular complex was found to selectively label MCF-7, potentially serving as a cancer cell detection marker. MCF-7 cells were detected with specific and strong FITC signals after only 4min of contact with the stain. The signals were about seven times stronger than that of a labeling performed on conventiona...

Biomicrofluidic lab-on-chip device for cancer cell detection

A lab-on-a-chip microfluidic device was designed, fabricated, and tested to be used in cancer cell or disease cell detection in body fluids. Mixtures of breast cancer cells MCF-7 and control cells MCF-10A were captured by meandering weir filters in microfluidic channels. A selective fluorescent complex 17β-estradiol-bovine serum albumin-fluorescein isothiocyanate enabled to specifically detect MCF-7 after only 4 min of contact. These signals are about seven times stronger than that of a labeling performed on conventional glass slides following the same protocol. The simple method could have the potential to replace complex existing cancer or disease detection schemes.

Nucleic Acid Sample Preparation from Dengue Virus Using a Chip-Based RNA Extractor in a Self-Contained Microsystem

Dengue fever (DF) and its more severe forms, dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) are the commonest arthropod-borne diseases affecting tropical or subtropical countries worldwide including Singapore. Currently, the diagnosis of dengue fever is usually made based on the clinical features, and confirmed by serology or by the reverse transcription PCR (RT-PCR) method. However, more than 50% of infected individuals are either asymptomatic or have an influenza-like undifferentiated fever. Therefore a rapid and sensitive method for the early detection of dengue virus infection is needed to improve disease management and outbreak control.