Real lab failures, root causes, and fixes — curated and bilingually annotated by our team.
Fluorescence reader displays negative values, which is physically impossible
Inconsistent or inaccurate readings caused by temperature variations in samples, standards, or reagents
Qubit Fluorometer screen becomes unresponsive, freezes, or instrument will not turn on
Qubit Fluorometer shows unexpected concentration values that do not match expected sample concentration
Qubit Fluorometer reading decreases when taking multiple measurements or reading after extended time
Qubit Fluorometer quantification value is significantly lower than UV absorbance (NanoDrop) measurement for the same sample
Qubit Fluorometer screen indicates samples are OUT OF RANGE (too low), sample fluorescence below lowest standard
Qubit Fluorometer screen indicates samples are OUT OF RANGE (too high), sample fluorescence exceeds highest standard
Qubit Fluorometer displays 『Standards Incorrect』 error message during calibration or measurement
Significant cell death observed following transfection with Lipofectamine RNAiMAX reagent
Cell toxicity observed during mRNA transfection experiments with MessengerMAX reagent
Light granular orange background fluorescence observed after GFP transfection with Lipofectamine 2000
Small granular precipitate visible microscopically on cells after adding transfection complexes
Transfection efficiency shows high variability between experiments and among replicates
Reduced cell viability and cell death observed following transfection procedure
Transfection efficiency is significantly lower than expected with poor gene expression
Transfection reagent was frozen instead of stored at 4°C, potentially affecting performance
Primers that initially worked successfully for PCR gradually fail or produce poor results after storage
Very few or no colonies obtained when subcloning PCR products generated with primers containing restriction enzyme sites, despite successful amplification
PCR fails to amplify templates with high GC content or produces very low yields
Ethidium bromide-stainable material remains in the gel wells and does not migrate during electrophoresis
PCR produces a band of incorrect size or sequence not matching the expected target
No bands visible on gel electrophoresis after PCR amplification
Desired PCR fragment appears faint or barely visible on gel electrophoresis
Gel electrophoresis shows smeared or streaked bands instead of distinct sharp bands
Multiple unwanted bands appear on gel electrophoresis alongside or instead of the desired PCR product
Recurring fungal contamination in cultures after incubation. Multiple cultures affected over time. Visible mold growth may appear on incubator surfaces. Persistent contamination despite replacing affected cultures.
Multiple cultures becoming contaminated simultaneously or in sequence. Contamination spreading despite apparently good technique. Cross-contamination between neighboring cultures.
Poor cell growth, cell death, or altered cell behavior without visible microbial contamination. May include effects from free radicals, metal ions, disinfectant/detergent residues, or endotoxins persisting after bacterial contamination is cleared.
Unexplained cell detachment, poor cell health, or cell death. Non-cytopathic viruses may show no obvious signs. Cannot be detected by conventional light microscopy. May not present significant effects if virus is host/tissue-restricted.
Visible turbidity and color change of medium. Fungal structures visible under standard light microscopy. Rapid onset similar to bacterial contamination. May include visible mold growth.
Slowed cell growth, altered cellular metabolism, chromosomal aberrations, and interference with cell attachment. No visible turbidity in medium. Difficult to detect by light microscopy due to small size (0.15-0.3 µm).
Rapid-onset turbidity and color change of culture medium (when phenol red is present). Medium becomes cloudy and pH indicator changes color quickly.
Previously working assay fails completely when switching to different master mix brand; positive controls fail; original master mix works but new one does not despite similar specifications
Variable and incorrect standard curve efficiency when using serial dilutions; effect more pronounced when same dilution series stored at 4°C and reused; inconsistent differences between amplification plots; problem resolves when different operator uses different tubes
PCR efficiency calculated from standard curve is greater than 120%; ΔCq between 10-fold dilutions is much less than expected 3.3 cycles (e.g., 1.5 cycles); standard curve gradient indicates abnormally high efficiency
Low concentration data points do not fit linear standard curve profile; NTC shows amplification with lower Tm and broader melt peak than positive samples; primer dimers visible on gel, inversely proportional to template concentration
Low or absent fluorescence in both test sample and positive control; correct PCR product is visible on gel; one probe in multiplex shows consistently high background with no amplification signal; background fluorescence equivalent to water control
Positive control amplifies successfully but test sample known to contain target shows no amplification; undiluted template fails while dilutions may show improved amplification
Amplification plots are clearly abnormal with sections dipping below zero dR; data cannot be used as presented; plots appear distorted
Very low Cq values for concentrated samples; amplification plots are not regularly spaced and appear abnormal; background fluorescence is significantly higher; minimal fluorescence yield through the reaction
Cq data for standard curve dilutions are irregularly spaced; ΔCq between dilutions is inconsistent and decreases with increasing dilutions; replicates are precise but pattern is abnormal
Assay is insensitive and amplification plots look abnormal with pronounced drift of the baseline; fluorescence signals are weak or irregular
ReadyMix produces amplification in standard PCR but completely fails in real-time qPCR applications; equivalent products from other suppliers work well
JumpStart Taq ReadyMix does not work as well as similar products from different suppliers; amplification is weak or absent despite correct assay design
The measured ratio of positive to negative cells for a given marker appears inaccurate or inconsistent. Background signals are not correctly measured, leading to improper gating and incorrect population quantification.
Antibody binds non-specifically to cells of interest, resulting in noisy data and elevated background. True marker expression cannot be distinguished from non-specific binding events.
Isotype control fails to accurately represent the non-specific binding background of the test antibody. Background levels measured by isotype control differ significantly from actual test antibody background.
Data quality is inconsistent between runs or gradually deteriorates over time. Instrument performance metrics fall outside acceptable ranges, affecting sensitivity and accuracy of all measurements.
One fluorochrome's emission spectra spills over into another detector channel, creating false positive signals. Data appears contaminated with signals that do not represent true marker expression.
Even after compensation, background spread from spillover effects makes it difficult to determine appropriate gate boundaries. Positive and negative populations are not clearly separated in the detector of interest.
Control used does not address the main source of background in the experiment, leading to incorrect gating and data interpretation. Results are inconsistent or unreliable despite using controls.
Biological control (e.g., unstimulated sample in stimulation assay) shows unexpectedly high background, making it difficult to set clear positive/negative boundaries.
PCR reaction fails to produce expected amplification or yields significantly reduced product, despite optimized reagents and cycling parameters. The issue traces to suboptimal thermal transfer or contamination from the plastic vessel itself.
Quantitative PCR shows inconsistent Cq values or fluorescence intensities between technical replicates in different wells, despite identical reaction setup. Well-to-well variability exceeds acceptable coefficient of variation.
PCR tubes become crushed, collapsed, or deformed after thermal cycling, potentially causing sample loss or compromised seal integrity. Tubes may show visible damage especially when using tube strips.
After PCR program completion, plates or tubes are found melted or stuck to the thermal cycler block, making removal difficult and potentially damaging samples. Plastic shows signs of thermal degradation.
Visible reduction in reaction volume after thermal cycling, with condensation on tube caps or film. May result in concentrated reagents, failed reactions, or inability to recover product.
Individual tube caps become dislodged during thermal cycling, exposing samples to evaporation and potential contamination. Caps are found loose or completely separated from tubes after run completion.
Quantitative PCR shows weak fluorescence signal across all wells, making accurate quantification difficult. Signal intensity is lower than expected despite adequate template and reagent quality.
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