放射治療的主要作用是造成癌細胞遺傳物質的雙股螺旋斷裂，促進細胞自戕。傳統放射治療的缺點就是輻射造成周遭正常組織產生副作用。低能量的鄂惹電子(Auger electron)的好處是有效作用範圍是幾奈米以內，對周遭健康組織的影響可以降到最低。因此，鄂惹電子的射源99mTc是腫瘤治療上的一個好選擇。
本研究主要想利用雷射光鉗系統在分子層次定量放射線物質99mTc造成DNA雙股螺旋斷裂的效果。利用雷射光鉗系統，生物素修飾的Lambda DNA在15 pN張力下，觀察放射性99mTc是否影響Lambda DNA雙股螺旋斷裂的發生時間。放射性99mTc被標定於一種DNA插入配體(ligand)上，以便將放射性物質盡可能靠近DNA分子並有效造成DNA 雙股斷裂。我們利用maximum likelihood estimation (MLE) 及bootstrapping simulations來估計Lambda DNA的平均壽命期(mean lifetime)及其誤差範圍。在控制組，我們發現Lambda DNA的平均壽命期是62.7分鐘，其誤差(95%信賴區間)落在47.5到85.3分鐘範圍內。當環境中只有配體時，我們發現DNA平均壽命期是90.9 分鐘，誤差範圍從69.7到123.1 分鐘。在低放射活度的環境中，我們發現DNA平均壽命期是114.0 分鐘，誤差範圍從85.5到159.2 分鐘。在高放射活度的環境中，DNA平均壽命期是132.3 分鐘，誤差範圍從97.6到189.2 分鐘。
利用Lambda DNA的結構長度，我們可以瞭解配體插入DNA結構。控制組中Lambda DNA的結構長度是16.7 ± 0.2 μm (平均值±標準差)。當環境中只有配體時，結構長度是17.6 ± 0.3 μm。在低放射活度的環境中，結構長度是17.3 ± 0.5 μm；在高放射活度的環境中，結構長度是18.1 ± 0.9 μm。高輻射環境下，DNA結構長度的分布情況比其他實驗條件下的結果要寬，所以放射線破壞DNA結構完整性造成更多配體嵌入DNA 分子中。高輻射環境下DNA平均壽命期卻比控制組DNA平均壽命期長。所以我們要更深入研究這結果。
實驗室中，核醫藥物的劑量學一般使用質體DNA和膠體電泳的方式來定量。本研究利用膠體電泳定量99mTc標誌的插入體(Intercalator)對質體DNA造成的傷害。在水溶液中，低放射劑量的範圍內，99mTc一次衰變造成平均雙股螺旋斷裂是0.011 ± 0.005；在有1M dimethyl sulfoxide (DMSO)的水溶液中，平均雙股螺旋斷裂則降低到0.0005 ± 0.0003。同樣的環境下，99mTc一次衰變造成平均單股螺旋斷裂是0.04 ± 0.02；在1M DMSO的水溶液中，平均單股螺旋斷裂下降至原來的1/5。平均雙股螺旋斷裂降低95%代表雙股螺旋斷裂發生的機制主要是輻射造成的非直接效應(Indirect effect)，可能是放射性插入體在DNA 分子上的聚集作用所造成。利用無放射性插入體破壞放射性插入體的聚集作用，一次衰變造成單股螺旋斷裂的效果不變，但雙股螺旋斷裂則與DMSO存在下的值相同。所以，雙股螺旋斷裂主要是放射性插入體的群聚作用產生的非直接效應所造成。
冷凍DNA 樣本是一般保存DNA 的方式。可是冷凍會影響DNA 分子的完整性。對於奈米技術的應用，DNA 結構完整性的改變可能會造成無法預期的結果，而且冷凍對DNA結構完整性的影響也尚未明瞭。所以利用雷射光鑷子來研究冷凍(-20 ºC)和冷藏(4 ºC)的Lambda DNA。評估DNA結構完整性的方式是測量DNA分子在受力(5-35 pN)下能維持多久才發生雙股螺旋斷裂。在5 pN，冷凍DNA的平均壽命期是44.3分鐘，95% 信賴區間(CI) 是36.7- 53.6 分鐘。冷藏的DNA分子的平均壽命期是133.2分鐘 (95% CI: 97.8-190.1分鐘)。在15 pN，冷凍DNA的平均壽命期是10.8分鐘 (95% CI: 7.6-12.6分鐘)。冷藏的DNA分子的平均壽命期是78.5分鐘(95% CI: 58.1-108.9分鐘)。所以冷凍確實改變DNA結構完整性，而且無法利用連接反應(Ligation)恢復DNA結構。

Radiation therapy for cancer patients works by ionizing damage to nuclear DNA, primarily by creating DSB. A major shortcoming of traditional radiation therapy is the set of side effect associated with its long-range interaction with nearby tissues. Low-energy Auger electrons have the advantage of an extremely short effective range, minimizing damage to healthy tissue. Consequently, the isotope 99mTc, an Auger electron source, is currently being studied for its beneficial potential in cancer treatment. We examined the dose effect of a pyrene derivative 99mTc complex on lambda DNA by using dual-beam optical tweezers in aqueous solution. To quantify the yield of double-strand breaks (DSB) on DNA molecules per decay at a molecular level, we measured the sustaining time of DNA, which was stretched under constant force. Biotin-labeled nonfrozen linear form lambda DNA was connected to streptavidin-coated beads by which DNA molecules were sustained under 15 pN. Mean lifetimes of DNA strands sustained under 15 pN were determined by maximum likelihood estimates and variances were obtained through bootstrapping simulations. The mean lifetime of DNA without ligand was 62.7 min with a 95% confidence interval (CI) between 47.5 and 85.3 min. The mean lifetime of DNA with ligand was 90.9 min (95% CI: 69.7–123.1 min). The mean lifetime of DNA treated with low and high radiation was 114.0 min (95% CI: 85.5–159.2 min) and 132.3 min (95% CI: 97.6–189.2 min). Contour lengths of lambda DNA were calculated using the Worm-like chain model. The contour length of DNA without ligand was 16.7 ± 0.2 μm (average ± standard deviation) and that of DNA with ligand was 17.6 ± 0.3 μm. The contour lengths of DNA at low and high radiation were 17.3 ± 0.5 and 18.1 ± 0.9 μm, respectively. We determined that ligand intercalated to DNA because the contour lengths became longer when ligand existed in the solution. Radiation destroyed DNA integrities and more ligand was able to intercalate to DNA molecules because the distribution and standard deviation of contour lengths was spread out. Lifetimes at high radiation were longer than those under other conditions. We intend to conduct further research to verify these results.
Dosimetry of radioactive medicines is usually quantified through plasmid DNA via agarose gel electrophoresis. We examined the dose effect of a pyrene derivative 99mTc complex on plasmid DNA by using gel electrophoresis in aqueous solution. In aqueous solutions, the average yield per decay for DSB is 0.011 ± 0.005 at low dose range, decreasing to 0.0005 ± 0.0003 in the presence of 1 M dimethyl sulfoxide (DMSO). The apparent yield per decay for single-strand breaks (SSB) is 0.04 ± 0.02, decreasing to approximately a fifth with 1 M DMSO. The 95% decrease in the yield of DSB in DMSO indicates that the main mechanism for DSB formation is through indirect effect, possibly by cooperative binding or clustering of intercalators. In the presence of non-radioactive ligands at a near saturation concentration, where radioactive Tc compounds do not form large clusters, the yield of SSB stays the same while the yield of DSB decreases to the value in DMSO. DSBs generated by 99mTc conjugated to intercalators are primarily caused by indirect effects through clustering.
DNA samples are commonly frozen for storage. However, freezing can compromise the integrity of DNA molecules. Considering the wide applications of DNA molecules in nanotechnology, changes to DNA integrity at the molecular level may cause undesirable outcomes. However, the effects of freezing on DNA integrity have not been fully explored. To investigate the impact of freezing on DNA integrity, samples of frozen and non-frozen bacteriophage lambda DNA were studied using optical tweezers. Tension (5 to 35 pN) was applied to DNA molecules to mimic mechanical interactions between DNA and other biomolecules. The integrity of the DNA molecules was evaluated by measuring the time taken for single DNA molecules to break under tension. Mean lifetimes were determined by maximum likelihood estimates and variances were obtained through bootstrapping simulations. Under 5 pN of force, the mean lifetime of frozen samples is 44.3 min with 95% confidence interval (CI) between 36.7 min and 53.6 min while the mean lifetime of non-frozen samples is 133.2 min (95% CI: 97.8-190.1 min). Under 15 pN of force, the mean lifetimes are 10.8 min (95% CI: 7.6-12.6 min) and 78.5 min (95% CI: 58.1-108.9 min). The lifetimes of frozen DNA molecules are significantly reduced, implying that freezing compromises DNA integrity. Moreover, we found that the reduced DNA structural integrity cannot be restored using regular ligation process. These results indicate that freezing can alter the structural integrity of DNA molecules.

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