A team of researchers recently submitted a paper to the journal Trends in Analytical Chemistry that reviewed different nanotechnology-assisted microfluidic systems, specifically nanoparticles (NPs)-integrated microfluidic biosensors, for chemical and bioanalysis. The challenges and future outlook of these sensors are also discussed.
Study: Nanotechnology-assisted microfluidic systems platform for chemical and bioanalysis. Image Credit: luchschenF/Shutterstock.com
Importance of Biosensors and Microfluidic Systems
Biosensors are analytical devices that can effectively convert and magnify a biological reaction into a quantitative or semi-quantitative signal to detect specific chemical substances. These sensors have gained considerable attention owing to their high sensitivity, quick response, and reliability.
Microfluidics, also referred to as lab-on-a-chip (LOC), holds significant potential in analytical and biomedical chemistry owing to its ease of integration, quick analysis time, and low consumption of reagents. Microfluidic sensor chips can be used to accurately determine chemical elements, heavy metals, airborne NPs, bacteria and viruses, biomarkers, and cell size and type.
Significance of Nanomaterials in Microfluidic Biosensing
Nanomaterials, such as zinc oxide (ZnO) and quantum dots (QDs), are the most suitable option for the construction of functional transducers in biosensing systems owing to their unique optical and electronic properties.
The flexibility of biosensing systems concerning post-modification or functionalization can significantly improve the analytical performance for detecting the target. Currently, advancements in nanotechnology have enabled the integration of NPs with microfluidic sensors for the effective detection of specific targets.
Gold NPs represent an excellent choice for integration with point-of-care or LOC diagnostic systems owing to their unique chemical and physical properties. These NPs can enhance the limit of detection (LOD) and sensitivity of sensors. The localized surface plasmon resonance (LSPR) that occurs in gold NPs plays a critical role in the detection mechanism of biosensors.
The LSPR properties of gold NPs were used to detect bovine somatotropin (bST) using a gold NP-integrated poly(dimethylsiloxane) (PDMS) microfluidic chip. Similarly, a gold nanoprobe-based immuno-chromatography test strip (ICTS) was used extensively to detect malignant tumors and infections. Weak sensitivity to small molecules and ions is one of the major disadvantages of gold NPs.
Graphene Oxide (GO)
GO has recently gained considerable attention for biosensing applications owing to its tunable chemical and physical properties, effortless surface modification, high fluorescence quenching capability, and good biocompatibility. Reduced graphene oxide (rGO), a GO derivative, was used to synthesize an rGO/ polyethyleneimine (PEI) layer on a gold electrode for the sensitive and selective electrochemical detection of Escherichia coli. Similarly, a dual-modality plasmonic-electrochemical microfluidic biosensor was developed using cysteine-graphene hydrogel (Cys-RGO) to measure the human cardiac myoglobin (cMb).
QDs are semiconductor nanocrystals with exclusive optical and electronic properties due to their nanoscale diameters. QDs are used in the biosensor structure for signal amplification and surface modification due to their narrow and size-tunable spectra, extensive absorption spectrum, and high quantum yield.
Paper-based microfluidic with QD labeling and magneto-microfluidic platform with QD labeling was developed to detect cadmium (II) and α-fetoprotein (AFP). Additionally, QD-based molecularly imprinted polymers on a paper microfluidic chip can be used to determine phycocyanin.
Magnetic Nanoparticles (MNPs)
MNPs play a crucial role in enhancing the overall performance of the microfluidic system as they possess superparamagnetism property that originates from the magnetic materials in their core. MNPs are used in microfluidic systems for surface applications owing to their functionalization flexibility.
Functionalized magnetic beads act as mobile substrates for detecting biological molecules from sample solutions. For instance, MNPs bead-based fluorescent immunoassay was used to detect influenza A virus, dengue virus, and thrombin, while MNPs bead-based electrochemical immunoassay was utilized to detect rubella and dinophysistoxin-1 and brevetoxin B. Magnetic beads are also used as a label to detect a target. For instance, electrochemical immunoassay with MNPs labeling is used to detect glucose.
Carbon Dots (CDs)
Fluorescence CDs (F-CDs) have gained prominence for biosensing applications owing to their colorful photoluminescence, chemically inert nature, and convenient preparation. CD-assisted microfluidic biosensors are specifically suitable for the detection of heavy metal ions. For instance, a filter paper-based fluorescence ON–OFF biosensing platform can be used to determine mercuric and copper (II) ions. Additionally, a paper microfluidic device based on fluorescence detection and enzymatic reaction can detect lactate and glucose.
Mesoporous Silica Nanoparticles (MSNs)
MSNs can be used effectively in biosensing applications as they possess high chemical and physical stability, porous structure, and high surface area. The high surface area of MSNs makes them a suitable choice to immobilize therapeutic carriers and recognition elements. Microfluidic paper-based on modified MSNs can detect glutamate, lactate, and glucose, while microfluidic immunosensor-based amino-functionalized MSNs are used to determine the epidermal growth factor receptor (EGFR).
ZnO is a semiconductor with a wide bandgap and is used in different applications such as transparent conducting films varistors. ZnO can amplify the fluorescence intensity in sensitivity sensors without requiring complex processes. Thus, ZnO is used extensively as protein microarray substrates. Microfluidic chips based on ZnO nanowires and smartphone-based microfluidic platforms based on ZnO nanorod are utilized to detect AFP and avian influenza, respectively.
Nanocomposites are referred to as composites that contain at least a nanometer-sized phase. Nanocomposites possess increased chemical resistance, electrical conductivity, and improved mechanical properties as they are synthesized by combining NPs with other materials.
Microfluidic devices based on (graphene-polyaniline) G-PANI and microfluidic electrochemical immunosensor based on graphene oxide-chitosan (GO-Chit) nanocomposite can be used to detect glucose and cystatin C, respectively.
Future Outlook and Challenges associated with NP-integrated Microfluidic Biosensors
The unique properties of nanoparticles facilitate designing an extensive range of microfluidic devices with enhanced biosensing performance. The integration of NPs and microfluidics can potentially lead to the development of miniaturized biosensing systems platforms for industrial, medical, and environmental applications.
However, certain issues, such as the analysis of complex samples such as blood and seawater, and challenges related to the physical properties of NPs, are required to be addressed before using nanotechnology-assisted microfluidic systems in practical applications. Additionally, more efficient interdisciplinary cooperation is needed to bridge the technological gap for integrating microfluidic devices with smartphones to manufacture portable microfluidic devices to meet the rising demand in the future.
Hasanzadeh, M., Fattahi, Z. (2022) Nanotechnology-assisted microfluidic systems platform for chemical and bioanalysis. Trends in Analytical Chemistry. https://www.sciencedirect.com/science/article/pii/S0165993622001200?via%3Dihub