Small Mass-Change Detectable Quartz Crystal Microbalance and Its Application to Enzymatic One-Base Elongation on DNA

Pocketable Biosensor Based on Quartz-Crystal Microbalance and Its Application to DNA Detection

Quartz-crystal microbalance (QCM) is a technique that can measure nanogram-order masses. When a receptor is immobilized on the sensor surface of a QCM device, the device can detect chemical molecules captured by the mass change. Although QCM devices have been applied to biosensors that detect biomolecules without labels for biomolecular interaction analysis, most highly sensitive QCM devices are benchtop devices. We considered the fabrication of an IC card-sized QCM device that is both portable and battery-powered. Its miniaturization was achieved by repurposing electronic components and film batteries from smartphones and wearable devices. To demonstrate the applicability of the card-sized QCM device as a biosensor, DNA-detection experiments were performed. The card-sized QCM device could detect specific 10-mer DNA chains while discerning single-base differences with a sensitivity similar to that of a conventional benchtop device. The card-sized QCM device can be used in laboratories and in various other fields as a mass sensor.

Adsorption behaviors of salivary pellicle proteins onto denture base metals using 27-MHz quartz crystal microbalance

BACKGROUND

The adsorption of salivary pellicle proteins onto the material surface is key for denture plaque formation.

OBJECTIVE

We aimed to investigate the adsorption of bovine serum albumin (BSA) and mucin (MCN) onto denture base metal materials using a 27-MHz quartz crystal microbalance (QCM) method.

METHODS

A gold (Au), titanium (Ti), and cobalt chromium alloy (Co-Cr) sensors were employed for QCM measurements. Adsorbed amounts of BSA or MCN were calculated by observing the frequency decrease, and the apparent reaction rate, kobs, was obtained by the curve fitting of the frequency shift against the adsorption time.

RESULTS

The adsorbed amounts of BSA on Ti were significantly lower than those on Au and Co-Cr. For MCN adsorption, Au showed significantly greater amounts of adsorption than Co-Cr. The kobs of Ti for BSA adsorption was significantly smaller than for the Co-Cr. The kobs of Ti, and Co-Cr for MCN adsorption were significantly smaller than for the Au. A clear correlation was not determined between adsorbed amounts of BSA or MCN onto each sensor and the surface topography or contact angles.

CONCLUSIONS

The difference of denture base metals and the difference of salivary proteins influences the adsorption behavior of salivary proteins.

Strategic Approaches for Highly Selective and Sensitive Detection of Hg2+ Ion Using Mass Sensitive Sensors

Here we present a quartz crystal microbalance (QCM) sensor for the highly selective and sensitive detection of Hg²⁺ ion, a toxic chemical species and a hazardous environmental contaminant. Hg²⁺ ion can be quantitatively measured based on changes in the resonance frequency of QCM following mass changes on the QCM sensor surface. The high selectivity for Hg²⁺ ion in this study can be obtained using a thymine-Hg²⁺-thymine pair, which is more stable than the adenine-thymine base pair in DNA. On the other hand, gold nanoparticles (AuNPs) and their size-enhancement techniques were used to amplify the QCM signals to increase the sensitivity for Hg²⁺ ion. With this strategic approach, the proposed QCM sensor can be used to quantitatively analyze Hg²⁺ ion with high selectivity and sensitivity. The detection limit was as low as 98.7 pM. The sensor failed to work with other metal ions at concentrations 1000-times higher than that of the Hg²⁺ ion. Finally, the recovery does not exceed 10% of the original value for the detection of Hg²⁺ ion in tap and bottled water. The results indicate acceptable accuracy and precision for practical applications.

Bone Response to Titanium Implants Coated with Double- or Single-Stranded DNA

We aimed to evaluate in vivo bone response and in vitro apatite formation to titanium (Ti) implants, coated with double-stranded DNA (DNA-d) or single-stranded DNA (DNA-s), and to compare the influence in different structure of DNA, double strand and single strand on bone response and apatite formation. The bone responses to multilayered DNA-d/protamine or DNA-s/protamine coating implants were evaluated after implantation into the extracted sockets of rat maxillary molars. Apatite formation on either coating surface after immersion in simulated body fluid (SBF) was evaluated using the quartz crystal microbalance (QCM) method. DNA-d/protamine and DNA-s/protamine coatings produced more roughened and hydrophilic surfaces than untreated Ti. Animal experiments showed that higher bone-to-implant ratios were achieved 3 and 6 weeks after implantation using DNA-d/protamine and DNA-s/protamine coatings compared with Ti. QCM measurements revealed that each coating contributed to significant earlier apatite formation in SBF. We conclude that both DNA-d/protamine and DNA-s/protamine coatings enhanced early bone formation. We suggest that a DNA-multilayer coating is useful for the surface modification of a Ti implant.

Protein Adsorption to Titanium and Zirconia Using a Quartz Crystal Microbalance Method

Protein adsorption onto titanium (Ti) or zirconia (ZrO₂) was evaluated using a 27 MHz quartz crystal microbalance (QCM). As proteins, fibronectin (Fn), a cell adhesive protein, and albumin (Alb), a cell adhesion-inhibiting protein, were evaluated. The Ti and ZrO₂ sensors for QCM were characterized by atomic force microscopy and electron probe microanalysis observation, measurement of contact angle against water, and surface roughness. The amounts of Fn and Alb adsorbed onto the Ti and ZrO₂ sensors and apparent reaction rate were obtained using QCM measurements. Ti sensor showed greater adsorption of Fn and Alb than the ZrO₂ sensor. In addition, amount of Fn adsorbed onto the Ti or ZrO₂ sensors was higher than that of Alb. The surface roughness and hydrophilicity of Ti or ZrO₂ may influence the adsorption of Fn or Alb. With regard to the adsorption rate, Alb adsorbed more rapidly than Fn onto Ti. Comparing Ti and ZrO₂, Alb adsorption rate to Ti was faster than that to ZrO₂. Fn adsorption will be effective for cell activities, but Alb adsorption will not. QCM method could simulate in vivo Fn and Alb adsorption to Ti or ZrO₂.

Trend of telomerase activity change during human iPSC self-renewal and differentiation revealed by a quartz crystal microbalance based assay

Telomerase plays an important role in governing the life span of cells for its capacity to extend telomeres. As high activity of telomerase has been found in stem cells and cancer cells specifically, various methods have been developed for the evaluation of telomerase activity. To overcome the time-consuming procedures and complicated manipulations of existing methods, we developed a novel method named Telomeric Repeat Elongation Assay based on Quartz crystal microbalance (TREAQ) to monitor telomerase activity during the self-renewal and differentiation of human induced pluripotent stem cells (hiPSCs). TREAQ results indicated hiPSCs possess invariable telomerase activity for 11 passages on Matrigel and a steady decline of telomerase activity when differentiated for different periods, which is confirmed with existing golden standard method. The pluripotency of hiPSCs during differentiation could be estimated through monitoring telomerase activity and compared with the expression levels of markers of pluripotency gene via quantitative real time PCR. Regular assessment for factors associated with pluripotency or stemness was expensive and requires excessive sample consuming, thus TREAQ could be a promising alternative technology for routine monitoring of telomerase activity and estimate the pluripotency of stem cells.

High-frequency phase shift measurement greatly enhances the sensitivity of QCM immunosensors

In spite of being widely used for in liquid biosensing applications, sensitivity improvement of conventional (5-20MHz) quartz crystal microbalance (QCM) sensors remains an unsolved challenging task. With the help of a new electronic characterization approach based on phase change measurements at a constant fixed frequency, a highly sensitive and versatile high fundamental frequency (HFF) QCM immunosensor has successfully been developed and tested for its use in pesticide (carbaryl and thiabendazole) analysis. The analytical performance of several immunosensors was compared in competitive immunoassays taking carbaryl insecticide as the model analyte. The highest sensitivity was exhibited by the 100MHz HFF-QCM carbaryl immunosensor. When results were compared with those reported for 9MHz QCM, analytical parameters clearly showed an improvement of one order of magnitude for sensitivity (estimated as the I50 value) and two orders of magnitude for the limit of detection (LOD): 30μgl(-1) vs 0.66μgL(-1)I50 value and 11μgL(-1) vs 0.14μgL(-1) LOD, for 9 and 100MHz, respectively. For the fungicide thiabendazole, I50 value was roughly the same as that previously reported for SPR under the same biochemical conditions, whereas LOD improved by a factor of 2. The analytical performance achieved by high frequency QCM immunosensors surpassed those of conventional QCM and SPR, closely approaching the most sensitive ELISAs. The developed 100MHz QCM immunosensor strongly improves sensitivity in biosensing, and therefore can be considered as a very promising new analytical tool for in liquid applications where highly sensitive detection is required.

In situ monitoring of structural changes during formation of 30S translation initiation complex by energy dissipation measurement using 27-MHz quartz-crystal microbalance

Ribosome is a bionanomachine that facilitates an orderly translation process during protein synthesis in living cells. Real-time monitoring of conformational changes in ribosomal subunits in aqueous solution is important to understand the regulatory mechanism of protein synthesis, because conformational changes in ribosome in E. coli have been predicted to operate the switch from translation initiation to an elongation process during translation. We performed an energy dissipation measurement by using a quartz-crystal microbalance-admittance (QCM-A) technique for in situ monitoring of conformational changes in pre-30S translation initiation complex in response to the binding of fMet-tRNA(fMet) in aqueous solution. The addition of fMet-tRNA(fMet) caused changes in the physical property (increased dehydration and elasticity) in 30S ribosomal subunit in the presence of mRNA and IF2/guanosine 5'-triphosphate (GTP) on the QCM plate. Furthermore, two sequential changes triggered by the addition of fMet-tRNA(fMet) were observed in 30S ribosomal subunit bound to mRNA in the presence of IF2/GTP and IF3. These observations suggest that the structural changes in 30S ribosomal subunit caused by the binding of fMet-tRNA(fMet) with IF2/GTP in the presence of IF3 could act as a switch to regulate the orderly processing in the construction of translation initiation complex, because the structural distinction can be a guidepost in the process for the relevant biomolecules.

Adsorption study of pellicle proteins to gold, silica and titanium by quartz crystal microbalance method

Initial stage of biofilm formation is the adhesion of salivary pellicle proteins on the material surfaces. The aim of the present study was to evaluate the adsorption behaviors of saliva pellicle proteins onto a gold, silica and titanium by using the 27 MHz quartz crystal microbalance method. As pellicle proteins, lactoferrin, lysozyme, defensin and mucin were evaluated. Adsorption amount of lactoferrin to silica was significantly lower than gold and titanium. Significant differences were detected between titanium and silica for the adsorption amounts of lysozyme. Chemical bond formation of sulfur atom of lysozyme and gold could be suggested. There were no significant differences of the adsorption amount of β-defensin among each substrate. For mucin adsorption, gold showed the highest adsorption amount. It is presumed that electrostatic repulsion caused less adsorption amounts of mucin to titanium and silica. In conclusion, the differences of the adsorption behaviors of pellicle proteins could be clearly identified.