Frequently Asking Questions (FAQs)
1. Assay Setup & Sample Preparation
What should I do if my sample RNA/DNA volume is less than 5 µL?
The standard volume of template nucleic acid added to the reaction is 5 µL. If your available sample volume is less than 5 µL, bring the volume up to 5 µL using the Nuclease-Free Water (NCS) provided with the kit. The final total reaction volume must be 20 µL.
Which nucleic acid extraction kits are recommended for sample preparation?
For RNA targets, spin-column or magnetic bead-based purification kits providing high purity—such as the Norgen Biotek Plant/Fungi RNA Isolation Kit (Cat# 25800) or equivalent systems—are recommended.
For DNA target, high-yield spin-column or magnetic bead-based genomic DNA extraction kits—such as the Norgen Biotek Genomic DNA Isolation Kit (Cat# 24700) or equivalent systems—are highly recommended.
For viral DNA or RNA targets, GRS Viral DNA/RNA purification kit (#GK12.0100) is highly recommended.
Should I keep the Passive Reference Dye (ROX) option enabled on my real-time PCR instrument?
No, it must be disabled (set to "None" or "Off"). The probes in this assay utilize non-fluorescent "dark" quenchers. Furthermore, if the ROX channel is actively assigned as a passive reference dye in your instrument software, it will lead to calculation errors or distorted baseline signals.
2. Instrument-Specific Setup & Channel Configuration
How should I configure channel assignments and software settings across different qPCR instruments?
Prior to running the assay, ensure that your real-time PCR instrument software is properly configured according to its specific optical layout and channel routing parameters.
- General Thermocycler Parameters: Program a total reaction volume of 20 µL (or 25 µL for LyoKit systems), with fluorescence data collection strictly enabled during the 60°C Annealing/Extension step across all active channels.
- Applied Biosystems (ABI) 7500 / 7500 Fast / QuantStudio Series: Set the experiment type to Standard Curve or Qualitative / Presence-Absence. In the target dye assignment section, map the target sequence to FAM and the Internal Control (IC) to Cy5. Under the Passive Reference drop-down menu, manually change the selection from ROX to None. Depending on your chosen thermal profile, select Fast or Standard ramp speed.
- Bio-Rad CFX96 / CFX Opus 96: Set the acquisition mode to All Channels. Assign FAM to Fluorophore Channel 1 and Cy5 to Fluorophore Channel 5. Ensure that no reference dye normalization is enabled in the plate setup layout.
- Rocgene Archimedes Setup: For Rocgene Archimedes series real-time PCR platforms, assign FAM, HEX/VIC, ROX, and Cy5 to their respective target channels, ensure the Passive Reference setting is set to "None", select "Dark Quencher", and program the software to collect fluorescence data at the 60°C Annealing/Extension step for a total reaction volume of 20–25 µL.
Roche LightCycler Setup: Detection Format & Color Compensation
For Roche real-time PCR platforms (LightCycler 480 I/II), configuring the correct Detection Format and applying Color Compensation is essential.
1. Detection Format Configuration
Select the correct optical filter combinations under the Detection Format menu:
- Format Selection: Select "Hydrolysis Probe", "Dual Color Hydrolysis", or "Multi Color Hydrolysis".
- Filter Combination Assignments:
- FAM Channel: 465–510 nm
- Cy5 Channel: 618–660 nm
- HEX / VIC: 533–580 nm
- ROX / Texas Red: 533–610 nm or 580–610 nm
- Melt Curve Disabled: Ensure the Melt Curve step is turned off. Set data acquisition exclusively at the 60°C Annealing/Extension step.
2. Color Compensation
- When to Apply: Strongly recommended for Multiplex Assays when running two or more dyes simultaneously. Not required for Monoplex Assays.
- How to Apply: In the Abs Quant or Qualitative Analysis module, check the "In Control / Apply Color Compensation" box and select the appropriate .ccf file.
3. Detector & Dye Setup (Channel Assignment)
What are the optical channel assignments, fluorophores, and wavelength specifications for this assay?
Define the target channels in your real-time PCR software as follows:
| Channel / Filter Set | Excitation (λex) | Emission (λem) | Target Selection | Reporter Dye | Quencher Type |
|---|---|---|---|---|---|
| FAM Channel | ~470 nm | ~520 nm | Target 1 | FAM | Dark Quencher |
| HEX / VIC Channel | ~533 nm | ~572 nm | Target 2 | HEX / VIC | Dark Quencher |
| ROX / Texas Red | ~577 nm | ~620 nm | Target 3 | ROX / Texas Red | Dark Quencher |
| Cy5 Channel | ~645 nm | ~697 nm | Internal Control | Cy5 | Dark Quencher |
4. Data Analysis & Result Interpretation
How does a POSITIVE result appear on the real-time PCR software display?
For a Positive result:
- FAM Channel (Target Gene): Generates a characteristic sigmoidal (S-shaped) amplification curve that intersects the threshold line with a Ct<35 (or the kit-defined threshold cutoff).
- Cy5 Channel (Internal Control / IC): May show an amplification curve or remain flat (No Ct) due to preferential amplification of high target template concentration. As long as the FAM channel is Ct<35, the sample is verified as POSITIVE.
How does a NEGATIVE result appear on the real-time PCR software display?
For a Negative result:
- FAM Channel (Target Gene): Shows no amplification curve (flat line / No Ct) or remains below the threshold line (Ct≥35).
- Cy5 Channel (Internal Control / IC): Must show a distinct sigmoidal amplification curve with a Ct<35, confirming successful nucleic acid extraction and PCR reaction performance. The combination of FAM (- / Ct≥35) and Cy5 (+) validates the sample as NEGATIVE.
What does it mean if both the Internal Control (Cy5) and Target Gene (FAM) show no signal (No Ct)?
This indicates an INVALID test result. Flat lines across both channels signify severe PCR inhibition, failed nucleic acid extraction, or omitted reagents. Do not report these samples as "Negative." Dilute the extracted sample 1:5 or 1:10 with Nuclease-Free Water and repeat the assay.
How should I read the Representative Amplification Plot on the qPCR software display?
On the qPCR amplification plot, the Y-axis measures fluorescence intensity (RFU), while the X-axis tracks the cycle number. Sigmoidal (S-shaped) curves crossing the threshold line indicate positive amplification, whereas flat lines remaining baseline represent negative results. The curve profiles and key plot parameters are illustrated below:
Axes & Core Parameters
- Y-Axis — Fluorescence (RFU): Represents the Relative Fluorescence Units, measuring the emitted fluorescence intensity generated as the target sequence amplifies during each cycle.
- X-Axis — Cycles (1 – 40): Indicates the total number of thermal cycles executed during the run.
- Threshold Line (Dot Line): Defines the calculated limit set above the baseline background noise. The cycle number at which the fluorescence curve crosses this line is determined as the Ct (Threshold Cycle) value.
Detailed Curve Profiles & Signal Evaluation
- 1. FAM: Positive Target [Ct<35]
- Profile: Shows a clear exponential phase leaving the baseline noise, ascending rapidly into a characteristic sigmoidal (S-shaped) curve, and intersecting the threshold line.
- Interpretation: Indicates the successful amplification of the target nucleic acid (DNA/RNA). Because the curve crosses the threshold line with a Ct value under the established cutoff (Ct<35), the sample is confirmed POSITIVE.
- 2. Cy5: Internal Control / IC [Ct<35]
- Profile: Displays an independent sigmoidal curve that crosses the threshold line prior to Ct=35.
- Interpretation: Serves as the process control. This amplification verifies efficient nucleic acid extraction and confirms the absence of PCR inhibitors in the reaction matrix.
- 3. FAM: Negative / No Ct
- Profile: Remains entirely flat along the baseline throughout all 40 cycles, showing no exponential signal increase and never reaching the threshold.
- Interpretation: Confirms the absence of the target pathogen/gene. When accompanied by a valid positive Cy5 Internal Control curve (Ct<35), the sample is formally reported as NEGATIVE.